# Mid-infrared Single-photon Detection Using Superconducting NbTiN Nanowires
with Sub-15 ps Time Resolution in a Gifford-McMahon Cryocooler

Jin Chang  Optics Research Group, ImPhys Department, Faculty of Applied
Sciences, Delft University of Technology, Delft 2628 CJ, The Netherlands.
Single Quantum B.V., Delft 2628 CJ, The Netherlands.  _Corresponding
<EMAIL_ADDRESS>Johannes W. N. Los  Single Quantum B.V., Delft
2628 CJ, The Netherlands.  Ronan Gourgues  Single Quantum B.V., Delft 2628 CJ,
The Netherlands.  Stephan Steinhauer  KTH Royal Institute of Technology,
Department of Applied Physics, Albanova University Centre, Roslagstullsbacken
21, 106 91 Stockholm, Sweden  S. N. Dorenbos  Single Quantum B.V., Delft 2628
CJ, The Netherlands.  Silvania F. Pereira  Optics Research Group, ImPhys
Department, Faculty of Applied Sciences, Delft University of Technology, Delft
2628 CJ, The Netherlands.  H. Paul Urbach  Optics Research Group, ImPhys
Department, Faculty of Applied Sciences, Delft University of Technology, Delft
2628 CJ, The Netherlands.  Val Zwiller  KTH Royal Institute of Technology,
Department of Applied Physics, Albanova University Centre, Roslagstullsbacken
21, 106 91 Stockholm, Sweden  Iman Esmaeil Zadeh  Optics Research Group,
ImPhys Department, Faculty of Applied Sciences, Delft University of
Technology, Delft 2628 CJ, The Netherlands.

###### Abstract

Shortly after their inception [1], superconducting nanowire single-photon
detectors (SNSPDs) became the leading quantum light detection technology [2].
With the capability of detecting single-photons with near-unity efficiency [3,
4, 5], high time resolution [6, 7], low dark count rate [8], and fast recovery
time [9], SNSPDs outperform conventional single-photon detection techniques.
However, detecting lower energy single-photons (<0.8 eV) with high efficiency
and low timing jitter has remained a challenge. To achieve unity internal
efficiency at mid-infrared wavelengths, previous works [10, 11] used amorphous
superconducting materials with low energy gaps at the expense of reduced time
resolution (close to a nanosecond [12]), and by operating them in complex mK
dilution refrigerators. In this work, we provide an alternative approach with
SNSPDs fabricated from 5-9.5 nm thick NbTiN superconducting films and devices
operated in conventional Gifford-McMahon (GM) cryocoolers. By optimizing the
superconducting film deposition process, film thickness and nanowire design,
our fiber-coupled devices achieved > 70% system detection efficiency (SDE) at
2 µm and sub-15 ps timing jitter. Furthermore, detectors from the same batch
demonstrated unity internal detection efficiency at 3 µm and 80% internal
efficiency at 4 µm, paving the road for an efficient mid-infrared single-
photon detection technology with unparalleled time resolution and without mK
cooling requirements. We also systematically studied the dark count rates
(DCRs) of our detectors coupled to different types of mid-infrared optical
fibers and black-body radiation filters. This offers insight into the trade-
off between bandwidth and dark count rates for mid-infrared SNSPDs. To
conclude, this paper significantly extends the working wavelength range for
SNSPDs made from polycrystalline NbTiN to 1.5-4 µm, and we expect quantum
optics experiments and applications in the mid-infrared range to benefit from
this far-reaching technology.

## Introduction

Detecting light at the single photon level has enabled novel scientific and
industrial applications in recent decades [2]. Specifically, near- and mid-
infrared detection are crucial for areas such as infrared fluorescence and
spectroscopy [13, 14, 15], semiconductor and industrial production monitoring
[16, 17], planetary soil studies [18], remote light detection and ranging [19]
as well as two-photon entanglement and interference [20] experiments. However,
since photon energy is inversely proportional to wavelength, detecting long
wavelength photons is intrinsically more challenging than detecting shorter
wavelength photons. Generally, Si-based detectors can be used for infrared
detection but suffer from a low cut-off wavelength, typically around 1.1 µm
[21], making them inefficient for long wavelength photon detection. Si:Sb
based impurity band conduction detectors show mid-infrared light detection
capability but not at the single-photon level [22]. Similarly, narrow-bandgap
photoconductive semiconductors, like HgCdTe, InAs and InGaAs detectors suffer
from low efficiency, large dark counts and poor time resolution [23]. In
contrast, SNSPDs have high detection efficiency [3, 4, 5], high detection
rates [24], low dark count rates (DCR) [8], unprecedented temporal resolution
[7, 6] and thus outperform traditional infrared single-photon detectors.

In 2001, NbN-based SNSPDs were first demonstrated by detecting 810 nm single-
photons [1]. Subsequently, SNSPDs fabricated on different platforms were
explored and developed [2]. Although high system detection efficiencies have
been realized and reported for the UV [25], visible [26] and near-
infrared/telecom [27, 3, 4, 5], detecting single-photons beyond 1550 nm with
high efficiency and time resolution has remained a challenge [28]. Early works
showed amorphous WSi based SNSPDs could be used for mid-infrared detection.
However, these studies employed 4-6 nm thin superconducting films, resulting
in low critical currents which is detrimental to the timing jitter. The
reported temporal resolution was close to the nanosecond scale [12]. Also,
these devices must be operated at sub-Kelvin temperatures, requiring complex
dilution refrigerators. NbN-based SNSPDs with ultra-narrow line widths showed
sensitivity up to 5 µm (saturated internal efficiency until 2.7 µm) [29]. A
consequence of squeezing the nanowire width to around 30 nm makes fabrication
challenging and degrades the detectors’ time resolution with the reduced
critical current.

Alternatively, our previous work [30] showed that by optimizing the
stoichiometry of polycrystalline NbTiN film during reactive magnetron co-
sputtering deposition, it is possible to make SNSPDs with strongly saturated
efficiency plateaus in the near-infrared region at 2.8 K operating
temperature, and also high performance at visible wavelengths up to 7 K [31].
Also, relatively thick NbTiN superconducting films were used [6, 32] to
improve our detectors’ optical absorption and critical current, therefore
enhancing efficiency and time resolution. Building on our previous results, in
this work we made SNSPDs from 5, 6.5, 7.5 and 9.5 nm thick NbTiN films with
different nanowire designs. First, by characterizing our SNSPDs using flood
illumination, we optimized the meander design in terms of internal detection
efficiency. Encouraged by our initial characterization results, we fabricated
fiber-coupled SNSPDs and achieved a system detection efficiency of >70% at 2
µm in Gifford-McMahon (GM) cryo-coolers (2.4-2.8 K). Broadband detectors were
also demonstrated with >50% SDE over the entire 1550-2000 nm range with sub-15
ps timing jitter. Furthermore, devices made from 7.5 and 6.5 nm films showed
unity internal detection efficiency at 3 µm and 80% internal efficiency at 4
µm. We also systematically studied the DCRs from the detector itself
(intrinsic DCRs) and from black-body radiation delivered by different types of
fibers as well as coated fibers as a technique to reduce the DCR. These
results offer a comprehensive understanding of the origin of dark counts in
mid-infrared SNSPD systems.

##  1 SNSPD Fabrication and Measurement Setup

Similar to [30], we deposited superconducting NbTiN films by a reactive
magnetron co-sputtering deposition process. The stoichiometry of the films was
controlled by adjusting the sputtering powers on the Ti and Nb targets. Film
thickness was determined by a calibrated crystal microbalance and SNSPDs were
fabricated as described in [6]. Our fabricated detectors were either tested
under flood illumination (figure 1 (a)), or etched into a key-hole die shape
and packaged using a standard ferrule and mating sleeves approach [33] (figure
1 (b)). This coupling method guarantees automatic alignment between detector
and optical fibers for accurate system efficiency measurements. Both the flood
illumination and fiber-coupled setup are shown in figure 1 (c).

Figure 1: Illustration of (a) detector flood illumination, (b) a fiber-coupled
detector, and (c) schematic of the efficiency measurement set-up.

As shown in figure 1 (c), we employ a near-infrared tunable laser (JGR-TLS5,
1260-1650 nm) and mid-infrared CW lasers with different wavelengths (2000 and
2700 nm laser from Thorlabs, 3001 and 4013 nm laser from Nanoplus) as input
photon sources. Single mode optical fibers are used to couple the light to the
first fiber-to-fiber coupler (containing neutral density filters and a
polarizer). A beam splitter is then used to create a reference arm with the
majority of the power coupled to a calibrated power meter $P_{1}$. The signal
beam with the lowest power is sent to the second fiber-to-fiber coupler, also
containing a polarizer and neutral density filters. A polarization controller
is used to tune the polarization state of the light after the second fiber-to-
fiber coupler. After recording the light power intensity emerging from the
polarization controller with power meter $P_{2}$, the light is guided to the
system to carry out either flood illumination or fiber-coupled measurements.
For flood illumination measurements, the input light is heavily attenuated to
the single-photon regime. For fiber-coupled device measurements we use the
following procedure: we first set the ratio $P_{1}/P_{2}$ to 50 dB by placing
ND (neutral density) filters in both fiber-to-fiber couplers, and then add
additional ND filters to the first coupler to reach $P_{1}$ = 10 nW. In this
way, the input photon flux can be back calculated. For example, 10 nW with 50
dB attenuation at 2000 nm corresponds to an input photon flux of $1.006\times
10^{6}$ photons per second. More measurement details can be found in our
previous work [4].

##  2 Characterization of SNSPDs with Flood Illumination

In this work, SNSPDs with different nanowire widths (40/60/80 nm) and
diameters (8/9/10 µm) were fabricated from 5-9.5 nm thick NbTiN films. For
example, 60-120-r4 refers to a meandering nanowire design with 60 nm wide
lines, a pitch of 120 nm, and 4 µm radius (see insert in figure 3 (b)).

Figure 2: Internal efficiency measurements of SNSPDs fabricated from (a) 9.5
nm and (b) 7.5 nm thick NbTiN films.

As shown in figure 2 (a), at 1550 and 1625 nm, the 40 nm width device
(yellow), 60 nm width device (green ) and 80 nm width device ( red ) all
showed saturated internal efficiencies. When the laser wavelength was
increased to 2000 nm, the 40 and 60 nm wide nanowires (yellow and green)
devices maintained saturated internal efficiencies, while the 80 nm wide
nanowire device (red curve) does not reach unity internal efficiency. To
obtain greater saturated internal efficiency, one possible solution is to make
narrower lines. However, with narrower line width (<40 nm) the nanofabrication
patterning, development, and etching, become more critical. This will, in
general, affect the fabrication yield. Alternatively, we sputtered 7.5 nm
thick NbTiN films and made detectors with the same designs and nanofabrication
process. As shown in figure 2(b), by using 7.5 nm thick NbTiN film, all
devices with line widths ranging from 40-80 nm showed unity internal
efficiency at 2000 nm. Detailed performance of devices based on 9.5 and 7.5 nm
films is summarized in table 1. A thinner film leads to lower critical
currents (for the same meander design), timing jitter is thus higher because
the output pulse has a lower signal to noise ratio [34]. The rise time (time
interval for signal to go from 20%-80% of the pulse amplitude) of the devices
on 7.5 nm NbTiN was longer than for the 9.5 nm devices and dead-time (width of
pulse at level of 1/e of the amplitude) was also slightly longer, this can be
explained by the fact that devices made with thinner films have higher kinetic
inductance.

Meander Structure |  $I_{c}$ (µA) 9.5/7.5 nm |  Rise-time (ps) 9.5/7.5 nm |  Dead-time (ns) 9.5/7.5 nm |  Jitter (ps) 9.5/7.5 nm
---|---|---|---|---
80-160-r4.5 |  25.0/18.4 |  350/375 |  9.3/10.6 |  30/44
60-120-r4 |  18.2/14 |  325/335 |  11.6/12.6 |  40/45
40-80-r5 |  8.40/6 |  400/425 |  38.4/49.2 |  93/97
|  |  |  |
Table 1: Flood illumination measurement results of 9.5 and 7.5 nm NbTiN based
SNSPDs. Figure 3: (a) Photon counting rate (PCR) curves at 2700 nm of
60-120-r4 detectors from 7.5 nm (green) and 9.5 nm (blue) film, (b) PCR curves
at 3001 nm of 60-120-r4 detector/purple and 1.1$\times$9 µm detector/red from
7.5 nm film, (c) PCR curves at 4013 nm of a 40-120-r5 detector from 6.5 nm
film, and (d) statistics of device yield made from films with different
thicknesses.

The above results show that saturated internal efficiency until 2000 nm can be
obtained with detectors made from 9.5/7.5 nm thick films. In order to explore
the internal saturation limit, we carried out longer wavelength flood
illumination measurements at 2700 and 3001 nm for a number of selected
detectors. Figure 3 (a) shows detectors with 60-120-r4 meander design from
both 9.5/7.5 nm films at 2700 nm. Both detectors reach unity internal
efficiency and detectors from 7.5 nm film (dark green curve) show stronger
saturated internal efficiency than detectors from 9.5 nm film (light blue
curve). This is because by reducing the thickness of the superconducting film,
the superconducting energy gap is reduced with the same input photon power, it
is easier to break the superconducting state and form a resistive region [35].

Previous measurements at 2700 nm indicate that detectors made from 7.5 nm
films are still promising for detecting single photons beyond 2700 nm, we
fabricated two types of SNSPDs from a 7.5 nm NbTiN film and measured their
detection performances at 3001 nm. As shown in figure 3 (b), a ’large’
meandering nanowire detector design of 60-120-r4 (purple), and a ’small’
detector design with line-width 60 nm, filling factor 50%, $1.1\times 9$ µm
(red) were employed. Both detectors show saturated internal efficiency at 3001
nm and the smaller detector shows superior saturated internal efficiency over
the larger one. According to a previous study [36], the performance of SNSPDs
is influenced by the inhomogeneity of the superconducting film. Since the
total length of the small detector ($\sim 90$ µm) is more than 3 times shorter
than the large ($\sim 418$ µm), less inhomogeneity can be expected and better
detection performance is observed. This shows that by reducing SNSPD’s total
length, better detection performance can be potentially achieved. In previous
works [11], the best performing device was a single 10-µm-long line. As a
consequence the active area is smaller, which can be increased by using
different detector architectures, for example multi-pixel [37] or interleaved
nanowire designs [38].

Finally, we evaluated detectors made from even thinner films (5 and 6.5 nm).
In figure 3 (c), we demonstrate that a detector (40-120-r5) from 6.5 nm film
achieves 80% internal efficiency at 4013 nm (determined using a sigmoid curve
fitting). This represents the state-of-the-art mid-infrared polycrystalline
material based SNSPDs. To get a better understanding of the film thickness on
the detector performance, we created an overview in figure 3 (d). We present
the statistics of 32 fabricated SNSPDs from 4 different films. It is clear
that 5 and 6.5 nm films suffer from low yield. The detectors made from the 5
nm films do not work well, because of their low critical current (1-2 µA). The
non-working detectors from the 6.5 nm film did not show unity internal
efficiency at 1550 nm possibly caused by lower film homogeneity of the thin
film [6]. In contrast, 7.5 and 9.5 nm films show higher yield but detectors
from the 9.5 nm film start to show decreased internal efficiency in the mid-
infrared compared to detectors from the 7.5 nm film. Here, we suggest two
practical solutions to solve the trade-off between film thickness and
performance for future mid-infrared SNSPDs study: Bias-assisted sputtering can
be applied to improve the critical current of SNSPDs [39] and post-processing
treatment (for example, helium ion irradiation [40]) can enhance the internal
efficiency of SNSPDs made from thicker films.

##  3 Measurements of Fiber-coupled SNSPDs

For most quantum optics experiments and applications, a fiber-coupled
detector/system is preferred because of mature fiber optics technology and
instruments.

Figure 4: Fiber-coupled SNSPDs measurements of (a) SDE of detector #1 at 1310,
1625, 1550 and 2000 nm,  (b) timing jitter of detector #1, (c) SDE of detector
#2 at 2001 nm, and (d) DCRs of detector #2 under different conditions: no
fiber (green), low-pass coated fiber (turquoise), UHNA fiber (red), and mid-IR
fiber (purple) plugged in.

The previous section provides evidence that both 7.5 and 9.5 nm NbTiN
superconducting films are suitable for making mid-infrared SNSPDs in terms of
good yield and internal efficiency while a reduced thickness (5-6.5 nm) leads
to fewer working devices. Thus, we fabricated fiber-coupled SNSPDs from 7.5 nm
thick NbTiN film. Similar to [4], the NbTiN films were initially deposited on
SiO2 grown by thermal oxidation process and nanowire meanders were eventually
located on top of a Au/SiO2 membrane acting as optical cavity. After packaging
and wire bonding, detectors were mounted in a closed-cycle cryocooler with a
base temperature of 2.4-2.8 K and coupled to single mode fibers. Afterwards,
lasers with different wavelengths were used for system detection efficiency
(SDE) measurements as described in the previous section.

Figure 4 (a) shows the performance of detector #1 (60 nm line width) made from
a 7.5 nm NbTiN film. The SDEs for 1300, 1550, 1625 and 2000 nm are 50%, 60%,
61%, and 63% respectively. The inset in figure 4 (a) shows detector #1’s
photon counting rate (PCR) curves at several wavelengths. Besides high SDE,
high timing resolution is also highly desirable for many applications, for
example, LiDAR [19], fluorescence microscopy and spectroscopy [14, 13]. The
Instrument Response Function (IRF) of detector #1 was characterized with a ps-
pulsed laser (4.2 ps pulse-width at 1064 nm wavelength) and a fast
oscilloscope (4 GHz bandwidth, 40 GHz sampling rate) as described in [4]. As
shown in figure 4 (b), using a low-noise cryogenic amplifier operated at 40 K,
the IRF of this device shows a Gaussian shaped histogram. After fitting, we
obtain 14.3$\pm$0.1 ps timing jitter (full width at half maximum, FWHM).
Compared to previous reported values for mid-infrared SNSPDs [12], we improved
time resolution by nearly two orders of magnitude. The inset picture in figure
4 (b) shows the pulse trace of detector #1. It shows a dead-time of 11.6 ns,
indicating good performance at high count rates [41]. Similarly, in figure 4
(c), we show the 2000 nm SDE measurement of detector #2, which is made from
another 7.5 nm NbTiN film but has a slightly higher meander filling factor
(approximately 10% higher). The benefit of a higher filling factor is an
increased optical absorption, which means if the internal efficiency is
saturated, a higher SDE can be achieved compared to a similar device with a
lower filling factor. As can be seen, detector #2 shows well saturated
internal efficiency (when Ib $\geqslant$ 0.8Ic). After sigmoid fitting (to
improve the efficiency estimation accuracy), we obtained a peak SDE over 70%
at 2000 nm.

Besides achieving high system detection efficiency, high dark count rates of
mid-infrared SNSPDs are a major challenge. Previous work [19] showed that the
DCRs of mid-infrared SNSPDs is typically in the order of $10^{4}$ Hz without
using additional filters. In figure 4 (d), we systematically studied the DCRs
of detector #2 in four different schemes: DCR without any fiber connected to
the detector (green curve), DCR with end-face coated SM2000 fiber (fiber
operating wavelength 1.7-2.3 µm, cyan curve), DCR with ultra-high NA fiber
without coating (fiber operating wavelength 1.5-2 µm, red curve) and DCR with
mid-infrared ZrF4 fiber without coating (fiber operating wavelength 2.3-4.1
µm, purple curve). As a result, at Ib=0.8Ic, the DCRs of detector #2 for the
above mentioned four schemes are around the order of 101 Hz, 102 Hz, 105 Hz
and 106 Hz, respectively. It is clear that the DCR of detector #2 when coupled
to an end-face coated fiber is 3 orders of magnitude lower than coupled to
ultra-high NA fiber without coating. By using this fiber end-facet coating
(low-pass filter), the DCR of detector #2 is below 240 Hz when it reaches
unity internal efficiency at 2000 nm. In contrast, when detector #2 is
connected to mid-infrared ZrF4 fiber for SDE measurements at 3-4 µm, the
detector showed over 2.78 MHz DCR at 0.8 Ic bias and starts latching [42].
This prevents further SDE measurements of detector #2 at 3-4 µm. To solve this
issue, low-pass filters should be employed before the detectors, either by
using fiber end-face coating, or adding cold filtering stages inside the
cryostat [43].

##  4 Discussion and Conclusion

In the past, amorphous materials were mainly used for mid-infrared single
photon detection motivated by the intuition that their superconducting energy
gap (0.59-0.61 meV for WSi [44]) is lower than polycrystalline material (2.46
meV for NbN [45]). This work pinpoints that NbTiN (polycrystalline) based
SNSPDs can also achieve high mid-infrared single photon detection efficiency
while maintaining unprecedented time resolution. Furthermore, given that the
energy of a single photon even at 10 µm wavelength (123.9 meV) is still
significantly larger than both materials’ superconducting energy gap, other
physical properties of the superconducting materials need to be investigated
to enhance SNSPDs’ mid-infrared detection response. Besides improving internal
detection efficiency, reducing the dark count rates is another outstanding
challenge for mid-infrared SNSPD systems. As shown in this work, only room
temperature black body radiation delivered to the detector by ZrF4 fiber has
led to >106 Hz DCR. To overcome this issue, either extra cryogenic filters
need to be added before the detectors or the entire experiment has to be
performed at cryogenic temperatures.

In conclusion, we demonstrated SNSPDs made from magnetron co-sputtered NbTiN
superconducting films (5-9.5 nm) with unity internal efficiency at 3 µm and
80% internal efficiency at 4013 nm when operated in closed-cycle Gifford-
McMahon coolers (2.4-2.8 K). Our fiber coupled device achieves over 70% system
detection efficiency at 2 µm and > 50% system detection efficiency from 1300
to 2000 nm with sub-15 ps time resolution. By employing an end-facet coated
fiber, the dark count rate of mid-infrared SNSPDs was reduced by 3 orders of
magnitude compared to uncoated single mode fibers. The DCR when coupled to
mid-infrared ZrF4 fiber is also studied, which offers valuable information for
building mid-infrared fiber-coupled SNSPDs systems in the future. To the best
of our knowledge, the detectors presented in this work have the best system
detection efficiency and temporal resolution among the mid-infrared SNSPDs
reported so far, and NbTiN is a solid choice for making mid-infrared SNSPDs
without mK dilution refrigerators.

## Acknowledgements

J.C. acknowledges China Scholarships Council (CSC, No.201603170247) . I.E.Z.,
V.Z., and Single Quantum B.V. acknowledge the supports from the ATTRACT
project funded by the EC under Grant Agreement 777222. R.B.M.G. acknowledges
support by the European Commission via the Marie-Sklodowska Curie action
Phonsi (H2020-MSCA-ITN-642656). S.N.D., S.S., V.Z. and Single Quantum B.V.
acknowledge EU FET-Open project funding (No. 899580). V.Z. acknowledges
funding from the Knut and Alice Wallenberg Foundation Grant “Quantum Sensors”,
and support from the Swedish Research Council (VR) through the VR Grant for
International Recruitment of Leading Researchers (Ref 2013-7152) and Research
Environment Grant (Ref 2016-06122).

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# The Future of Hybrid Meetings

Marios Constantinides  Nokia Bell LabsCambridgeUnited Kingdom
<EMAIL_ADDRESS>and  Daniele Quercia  Nokia Bell
LabsCambridgeUnited Kingdom<EMAIL_ADDRESS>
(2022)

###### Abstract.

Meetings are typically considered to be the fuel of an organization’s
productivity—a place where employees discuss ideas and make collective
decisions. However, it is no secret that meetings are also often perceived as
wasteful vacuums, depleting employee morale and productivity, likely due to
the fact that current technologies fall short in fully supporting physical or
virtual meeting experience. In this position paper, we discuss the three key
elements that make a meeting successful (i.e., execution, psychological
safety, and physical comfort), and present new tools for hybrid meetings that
incorporate those elements. As past research has focused on supporting meeting
execution (the first element), we set the roadmap for future research on the
two other elements: on psychological safety by articulating how new
technologies could make meeting useful for all participants, ensure all
participants give and receive appropriate levels of attention, and enable all
participants to feel and make others feel comfortable; and on physical comfort
by dwelling on how new technologies could make the meeting experience
comfortable by integrating all human senses. We also discuss the potential
danger of these technologies inadvertently becoming surveillance tools.

workplace, meetings, psychological safety, physical comfort

††journalyear: 2022††copyright: rightsretained††conference: 2022 Symposium on
Human-Computer Interaction for Work; June 8–9, 2022; Durham, NH,
USA††booktitle: 2022 Symposium on Human-Computer Interaction for Work
(CHIWORK), June 8–9, 2022, Durham, NH, USA††price: 15.00††doi:
10.1145/3533406.3533415††isbn: 978-1-4503-9655-4/22/06††ccs: Human-centered
computing Collaborative and social computing systems and tools

##  1\. Introduction

While meeting tools, to a great extent, have increasingly simplified and
augmented the ways meetings are conducted, they still fall short in supporting
the nuanced experience of offline meetings. To see why, consider, a virtual
all-hands meeting, where one would expect a one-to-many form of communication.
One could imagine that not everyone would feel comfortable sharing their video
streams in such a setting and, as such, the meeting host might miss the
opportunity to “read the room” (i.e., interpret non-verbal cues that are
generally expressed in offline settings). The interplay between offline and
online worlds has slowly but surely produced a new breed of meetings: _the
hybrid meeting_. This type of meeting typically involves a mixture of in-
person and remote attendees: remote attendees join the meeting via a virtual
meeting platform (e.g., Zoom), and in-person attendees sit together in the
typical meeting room. Meeting experience is therefore shaped not only by the
participants’ interactions but also by their diverse physical environments. In
this position paper, we:

  * •

Discuss the three key elements that make a meeting successful (Section 2).

  * •

Present recent research that incorporates those three elements (Section 3).

  * •

Set the roadmap for future research, focusing on the two elements out of the
three that are often neglected in the literature—psychological safety and
physical comfort (Section 4).

  * •

Discuss the potential danger of future meeting technologies inadvertently
becoming surveillance tools (Section 5).

##  2\. What makes meetings successful

Figure 1. Three key elements that make a meeting successful along with key
research questions for future research: (a) _Execution_ : whether the meeting
had a clear purpose, structure, and resulted in actionable items; (b)
_Psychological safety_ : whether participants felt listened to and were
motivated to contribute during the meeting; and (c) _Physical comfort_ :
whether participants felt physically comfortable by, say, being in an
environment with good air quality and sufficient natural light. Most
innovations in meeting technologies have focused on execution, and future work
should focus on the two other aspects - psychological safety and physical
comfort. A sample of key research questions are reported in this infographic.

A meeting’s perceived experience has been evaluated through standardized
questionnaires, or ad-hoc post meeting surveys. For example, the Event
Performance Indices (EPI) (Kerns, 2015) is a six-item questionnaire that
focuses on a meeting’s overall performance results, and, in turn, measures
meeting effectiveness. The questionnaire prompts participants’ satisfaction
levels including, for example, whether the meeting was worth the time
investment, and whether participants were personally motivated. In the fields
of Management and Organizational Science, meeting productivity has been
directly linked with a meeting’s agenda, structure, and purpose (Lent, 2015;
Cohen, 2016; Schwarz, 2016). Inclusiveness (Axtell, 2016, 2017), dominance
(Romano and Nunamaker, 2001), peripheral activities (Niemantsverdriet and
Erickson, 2017), and psychological safety (Grenny, 2017; Axtell, 2018) are
aspects that have also been found to influence meeting experience and
productivity. The physical comfort of the workplace environment is an
additional factor that makes up the list (Alavi et al., 2017). For example, a
recent survey found that light and outdoor views were among the most popular
perks employees craved for (Meister, 2018), whereas stuffy and stale air
offices tended to reduce productivity (Allen et al., 2016; Allen, 2017; Tom Y.
Chang and Neidell, 2016).

More recently, to capture the factors that generally make a meeting
successful, Constantinides et al. (Constantinides et al., 2020) designed a
28-question survey and administered it to 363 individuals whose answers were
then statistically analyzed. The survey covered an array of themes, previously
identified in the Organization and Management Science literature, including a
meeting’s psychological experience (e.g., contribution, balance, turn-taking,
attention), its structure, and its content (e.g., agenda, physical
environment, use of technology). The survey responses were then statistically
analyzed using a Principal Component Analysis, with 11 items of the
28-question survey explaining 62% of the total variance. These 11 items loaded
on three factors - the three factors that make a meeting successful:

:

Execution. Whether participants ultimately “got things done”—more
specifically, whether the meeting had a clear purpose, structure, and resulted
in actionable items.

:

Psychological Safety. Whether participants felt listened to and were motivated
to contribute during the meeting.

:

Physical Comfort. Whether participants felt physically comfortable by, for
example, be in a meeting room with good air quality and sufficient natural
light.

##  3\. Current Support For The Three Factors Determining Success

Next, we discuss recent research aiming at supporting these three key elements
in either physical or virtual meetings.

###  3.1. Execution

Execution refers to whether the meeting had a clear purpose, structure, and
resulted in actionable items. Besides the mainstream communication tools of
the likes of MS Teams, WebEx, Skype, Zoom, just to name a few, a large body of
scientific work has been focused on supporting meeting execution through
contextual information, text, audio, and video support. For example, one work
focused on detecting key decisions in dialogues (Kim and Rudin, 2014), while
another on generating an “action items” list from these dialogues (McGregor
and Tang, 2017). Using an agenda planning technique, Garcia et al. (Garcia et
al., 2004) developed a tool that allows meeting participants to vote for
agendas items. As the balance of conversational turn-taking is important for
group performance (Woolley et al., 2010), technologies were developed to
create awareness. This was done by highlighting salient moments and
visualizing participants’ contributions (Kim et al., 2008). Content recording
was also a focus for technologies supporting execution. NoteLook (Chiu et al.,
1999) exploited video streams to support note taking. Catchup (Tucker et al.,
2010) automatically identified the gist of what was missed in a meeting,
allowing people to join the meeting late and still participate effectively.
Video Threads (Barksdale et al., 2012) supported asynchronous video sharing
for geographically distributed teams. Finally, Banerjee et al.’s playback
system allowed for revisiting a recorded meeting (Banerjee et al., 2005).

###  3.2. Psychological Safety

Psychological safety refers to whether participants felt listened to and were
motivated to contribute during the meeting. As Edmondson described it,
psychological safety refers to “the absence of interpersonal fear that allows
people to speak up with work-relevant content” (Edmondson, 1999). In face-to-
face interactions (e.g., during a social encounter or a meeting), we primarily
read faces through visual cues and read bodies through a multi-sensory
integration. All these cues, to a great extent, allow us to understand the
dynamics in a conversation (e.g., whether one feels listened to and receives
the appropriate attention from his/her peers). In virtual interactions,
however, these natural cues are often lost, flattening the psychological and
social experience. Furthermore, current meeting technologies need to deliver
this experience in an attention-enhancing way as opposed to the current
attention-depleting way: currently, in a virtual meeting, attendees need to
pay attention not only to what is being said, but also to peripheral modes of
communication (e.g., text messages, raising of virtual hands).

To bring the offline meeting experience into the virtual world, recent
research developed an app called MeetCues. This captures three types of cues,
aiming at augmenting psychological safety in hybrid meetings. First, the
MeetCues app allows meeting attendees to provide real-time feedback (Aseniero
et al., 2020). The app enabled attendees to react on what was being discussed
by tagging key points and action items. These virtual crowdsourced tags were
translated into an emoji cloud visualization, which allowed attendees to infer
the overall atmosphere. In this way, these crowdsourced cues served as
indicators of moments during which, for example, participants agreed with what
was being said or whether further clarification was needed, cultivating a safe
environment for contributions.

However, these crowdsourced feedbacks did not fully capture the multi-sensory
integration that we are attuned to in physical meetings. A case in point is
the almost universally acceptable non-verbal cue of nodding (Peleckis and
Peleckienė, 2015). In face-to-face interactions, it is natural to observe
bodily expressions to understand, for example, whether one agrees on what is
being said (nodding), or a clarification is needed. However, the picture is
different in virtual meetings. Participants of virtual meetings who often turn
off their cameras, leave the speaker staring at a sea of black squares,
feeling psychologically disoriented.

That is why the second type of cues MeetCues captured was body movements. It
did so by integrating wearable devices with the MeetCues app, which captured
participants’ heart rates, head and hand movements, and changes in postures
(Choi et al., 2021; Park et al., 2020). These body cues were predictive of the
meeting’s vibrancy and multi-tasking activities, and ultimately of the
meeting’s success; these cues were even more predictive than the meeting’s
emotional content derived from the meeting’s transcript. For example, head
movements such as nodding served as a proxy for (dis)agreement, while changes
in postures served as a proxy for (dis)comfort. In particular, these two body
cues metrics proved useful in helping attendees infer the levels of
psychological safety “in the room”.

The third type of cues MeetCues captured was types of conversations (Choi et
al., 2020) (e.g., a heated discussion resulting in a conflict eventually being
resolved, a supportive conversation, an exchange of knowledge). By analyzing
more than four thousand minutes of conversations from eighty-five real-world
meetings, Zhou et al. (Zhou et al., 2021b) found that conversation types were
more predictive of meeting success than traditional voice and text analytics.
By monitoring these conversations during a meeting (or after it), one could
potentially measure specific aspects of organizational productivity, and
proactively take actions for improvement. To see how, consider conflict
resolution. Having new real-time ways of marking indicators of, for example,
conflicts, not only would increase attendees’ awareness but would also help
cultivate an approach of conflict resolution.

###  3.3. Physical Comfort

Physical comfort refers to whether participants felt physically comfortable
by, for example, be in a meeting room with good air quality and sufficient
natural light. To see what we mean by the word ‘comfort’, let us draw a
parallel with architecture. In that area, comfort mainly describes four main
qualities that a good building must possess: visually pleasurable, thermally
livable, acoustically tolerant, and respiratory humane (in terms of air
quality) (Alavi et al., 2017).

To paraphrase comfort in the meeting context, recent research has initially
focused on the specific aspects of good air quality and natural light. A team
of researchers, in particular, developed miniaturized devices, called Geckos,
which are fitted with cheap-to-produce sensors capturing light, temperature,
and the presence of a broad range of gases such as volatile organic compounds
(VOCs). They integrated Geckos with the MeetCues app (Aseniero et al., 2020),
and created a new indoor environmental sensing infrastructure ComFeel
(Constantinides et al., 2020). At the end of each meeting, the MeetCues app
asks each participant: _(a)_ whether the meeting had a clear purpose and
structure, and resulted in a list of actionable points, and _(b)_ whether each
participant felt listened to and was motivated to contribute.

To explore the extent to which air quality alone determined whether a meeting
was perceived to be productive or not, they deployed ComFeel in a corporate
office and gathered data from 29 meetings in different rooms. As one expects,
productive meetings were those in which participants felt safe to contribute:
the probability of a meeting being productive increased by 35% for each
standard deviation increase in psychological safety. Surprisingly, the results
for air quality were dramatic too. The productivity probability increased by
as much as 25% for each standard deviation increase in room pleasantness.
Furthermore, among all the sensors, the air quality one was the most
important: indeed, room pleasantness was achieved through improved temperature
(with a relative contribution of 25%), lighting (30%), and air quality (45%).
These results suggest that, if a meeting takes place in a stuffy conference
room, even if it is run well, people will still struggle to pay attention. To
fix that, one just needs to do a handful of things, from manually or
automatically adjusting ventilation, lighting, temperature, which could
increase a meeting’s productivity by a considerable extent.

##  4\. The three factors in Future Hybrid Meetings

Most innovations in meeting technologies have focused on supporting physical
or virtual meetings independently, and they did so by extensively focusing on
how to support meeting execution. That is why future work should focus on the
two other overlooked aspects (Figure 1): on psychological safety (Section
§4.1) by making meetings useful for all participants, ensuring all
participants give and receive appropriate levels of attention, and enabling
all participants to feel and make others feel comfortable; and on physical
comfort (Section §4.2) by integrating all human senses, and, as such, making
the meeting sensory experience pleasurable. At the same time though, future
work should also consider how these new technologies could inadvertently
become surveillance tools (Section §5).

###  4.1. Rethinking Psychological Safety

The design space of meeting technologies could be well enriched with features
that fully support all three facets of psychological safety (Constantinides et
al., 2020): _(a)_ making the meeting useful and satisfying for all
participants, _(b)_ ensuring all participants give and receive appropriate
levels of attention, and _(c)_ enabling all participants to feel and make
others feel comfortable.

First, to make a meeting useful and satisfying, existing tools already provide
analytics in the form of summaries or real-time feedback (Aseniero et al.,
2020). However, these analytics could be enriched with aspects that are hard
to quantify such as the types of conversations happening in a meeting (Zhou et
al., 2021b), nuanced emotional states (Zhou et al., 2022), or other language
markers that are hidden in conversations (e.g., presence of stress, engagement
in emphatic conversations) (Scepanovic et al., 2020; Robertson et al., 2019;
Zhou et al., 2021a).

Second, as turn-taking and balance in conversation helps to cultivate a safe
environment for contribution (Woolley et al., 2010), future meeting tools need
to ensure that all attendees give and receive the appropriate levels of
attention. For example, some meeting technologies already do provide
indicators about “speaking up” time, and often do so through attention-
depleting notifications. However, future technologies must ensure attention-
enhancing ways of notifying users. As Weiser and Brown argued in their seminar
work _The Coming Age of Calm Technology_ , “the information display should
move easily from the periphery of users’ attention to the centre, and back”
(Weiser and Brown, 1997). Future design elements need to smoothly capture the
user’s attention only when necessary, while calmly remain in the user’s
periphery most of the time. For example, while current meeting tools allow
various modes of communication (e.g., voice, text) and notifications (e.g.,
emojis) in a virtual meeting, personalized or timely delivery of those
notifications could remove unnecessary information overload. Imagine a
scenario during which five attendees need to focus on the speaker, yet one of
them types a question and another raises his/her virtual hand. If these
notifications were to be delivered straight away, they may well overload the
speaker and distract the audience. More work needs to go into identifying the
right moment for delivering a notification, or that for delivering a
notification to the best person in a group, allowing for personalized
delivery.

Third, it is also important for meeting technologies to facilitate an
inclusive environment where all attendees feel comfortable, and can make
others feel comfortable. One way of achieving it is to create social
interactions that scaffold learning, and then use computational methods to
weave these interactions into the fabric of meeting tools. For example, as
demonstrated in massive online classes (MOOCs) (Quintana et al., 2018), future
meeting technologies could coach people skills that foster inclusion and
diversity, and collaboratively help them reflect on their behavior. Another
way of achieving inclusivity is through broadening the design space. Design
elements such as emojis allow, to a great extent, attendees to non-verbally
communicate and express their emotional state; it can be seen as a way of
developing trust or empathy for others. Future meeting technologies could also
borrow concepts from biophilic design (Wilson, 1984) and embrace new types of
visual cues (Qin et al., 2020) (e.g., the use of different symbols, imagery,
and artificial artifacts), thus making additional layers of non-verbal
communication available to users.

###  4.2. Rethinking Physical Comfort

Aligned with the Human-Building Interaction vision (Alavi et al., 2019) (an
emerging area aiming at unifying HCI research in the built environment),
physical comfort goes well beyond air quality, integrating all the human
senses. To begin with, let’s take sight. Could we make the physical
environment visually pleasurable? Recent studies showed that adjusting light
conditions in a room could serve as a stress reducing intervention mechanism,
or even as a biofeedback relaxation training (Ren et al., 2019; Yu et al.,
2018). Moving to hearing. Could we design ubiquitous technologies that
facilitate meetings anywhere and everywhere? Consider a knowledge worker who
attends meetings from a variety of places: from the office to home to a
cafeteria to even an autonomous car (Kun et al., 2020). How could future
technologies support smooth transition between different places, and provide a
pleasurable sound experience? Smart earable devices can be one of the answers
wherein an array of sensors could be embedded in them to control not only what
sound the end user is hearing, but also how that sound is delivered in a
specific physical setting (Kawsar et al., 2018). While addressing sight and
hearing is to some extent easier, smell and touch require future research
efforts. Which odour is more relaxing and energizing during a meeting, and, to
what extent, certain odour could be adapted as a meeting unfolds to facilitate
better execution? How could we stimulate the sense of touch to increase
physical comfort during a meeting? For example, as most of white collar jobs
require employees to spend long hours sitting, previous studies explored the
design of ergonomic chairs that would increase physical comfort levels. While
these studies typically employ various objective methods to capture physical
comfort such as pressure sensors measurement (Zemp et al., 2015) or an array
of sensors including, for example, temperature, gas, illuminance, VOC, CO2
(Zhong et al., 2020), new sensing modalities such as Electromyography (EMG)
could prove useful to fully incorporate the sense of touch in the design space
of these chairs.

##  5\. The dangers of meeting technologies

While these technologies hold the promise of enabling employees to be
productive, report after report has highlighted the outcries of workplace AI-
based solutions being biased and unfair, and lacking transparency and
accountability. During the COVID-19 pandemic, systems were being used to
analyze footage from security cameras in workplace to detect when employees
are not complying with social distancing
rules111https://www.ft.com/content/58bdc9cd-18cc-44f6-bc9b-8ca4ac598fc8; while
there is a handful of good intentions behind such a technology, the very same
technology could be used for tracking employees’ movements, or time away from
desk. As we move towards a future likely ruled by big data and powerful AI
algorithms, important questions arise relating to the psychological impacts of
surveillance, data governance, leadership and organizational culture, and
compliance with ethical and moral concerns. The historian and philosopher
Yuval Noah Harari argued that digital platforms such as those that allow us to
work from remote need to follow three basic
rules222https://www.ft.com/content/f1b30f2c-84aa-4595-84f2-7816796d6841 to
protect us from “digital dictatorships”. First, any data collection on people
should be used to help people rather than to manipulate, control, or harm
them. In the meetings context, this translates into providing analytics that
help employees reflect on their experience rather than causing them to receive
low performance review in the event of a meeting not being executed well.
Second, surveillance must always go both ways. That is, whenever an
organization increases surveillance of individuals, at the same time,
organizational accountability needs to increase. If organizations could
establish processes to monitor their workforce, they may well establish
processes to audit their own actions as well. Third, data should not be
concentrated in a single entity, not least because data monopolies are the
recipe for dictatorship. In the workplace context, this translates into newly
created divisions in a company that oversee data collection and, ideally,
ensure that data about their workers is in the hands of the workers
themselves.

In a global modernized workplace, new meeting tools are likely to be
developed, facilitating and augmenting the experience of hybrid meetings. As a
result of the COVID-19 pandemic, fully remote or hybrid meetings removed any
physical barriers and often contributed to improved work-life balance
(Rudnicka et al., 2020). On the downside, tools for supporting hybrid meetings
may inadvertently becoming surveillance tools, compromising employees’ privacy
(Constantinides and Quercia, 2022). To unpack the AI ethics of workplace
technologies, Constantinides and Quercia (Constantinides and Quercia, 2022)
conducted a crowdsourcing study to understand how employees judge such
technologies and determine which ones are desirable, and why. They considered
16 workplace technologies that track productivity based on diverse inputs
(e.g., tracking audio conversation during virtual meetings, tracking text
messages in collaboration tools), and asked crowd-workers to judge these
scenarios along five moral dimensions. They found that workplace technologies
were judged harshly depending on three aspects (heuristics) participants used
to assess the scenarios. In increasing importance, these aspects reflected
whether a scenario: 1) was not currently supported by existing technologies
(_hard to adopt_); 2) interfered with current ways of working (_intrusive_);
and, more importantly, 3) was not fit for tracking productivity or infringed
on individual rights (_harmful_). Tracking eye movements in virtual meetings
and the visited websites in remote work, despite being possible, were
considered to be “on the way” of getting the job done (they were easy to adopt
but intrusive). By contrast, tracking text messages in collaboration tools
such as Slack was considered to not interfere with work (unobtrusive).
Finally, tracking audio conversations in virtual meetings was considered to be
possible (easy to adopt), and not interfere with work (unobtrusive), yet it
was considered to be harmful, as it entailed tracking not only whether a
meeting took place but also its content, causing a loss of control. The above
heuristics offer a guide on how workplace technologies are likely to be
morally judged. Having a technology that is easy to implement and does not
interfere with work is not necessarily a technology that should be deployed.
_Tracking facial expressions_ (even beyond the nefarious uses - of dubious
effectiveness - of inferring political orientation or sexual preferences (Wang
and Kosinski, 2018)) is possible and could be done in seamless ways (e.g.,
with existing off-the-shelf cameras), yet it would be still considered harmful
and unethical. _Tracking eye movements_ , _task completion_ , or _typing
behavior_ was considered a proxy for focus (harmless) yet intrusive as it
would “get in the way”. _Tracking social media use in remote work_ was
considered not only intrusive but also harmful, as it infringes on privacy
rights.

On a very pragmatic level, there is a handful of reasons as to why
organizations opt for employee surveillance (e.g., maintaining productivity,
monitoring resources used, protecting the organization from legal
liabilities). Critics, however, rightly argue that there is a fine line
between what organizations could be monitoring and what they should be
monitoring. If this line is crossed, it will have consequences on employees,
affecting their well-being, work culture, and productivity (Ball, 2010). If
future meeting tools incorporate any kind of employee monitoring, they need to
preserve individual rights, including that of privacy. New meetings tools need
to also ensure non-discrimination, while promoting inclusivity, and, at the
same time, provide explainable and understandable outputs (e.g., the decision
upon which the system decided that a meeting was successful or not).

Hybrid meetings also create asymmetries of interactions stemming from the
social and cultural contexts. As Saatci et al.(Saatçi et al., 2019) found, the
most challenging asymmetry is the diverse experience between co-located and
remote meeting participants. Remote participants often feel isolated, while
co-located participants dominate the interaction. Differences in language and
accent, cultural behaviors, digital literacy, physical location, and the
boundaries between work and personal life (Rudnicka et al., 2020) also
contribute to interaction asymmetries. To overcome such challenges, new
meetings tools should focus on making meetings more inclusive for everyone by
maximizing psychological safety and optimizing physical comfort.

###### Acknowledgements.

We thank those who actively supported this research at Nokia Bell Labs; in
particular, Sagar Joglekar, Bon Adriel Aseniero, and Jun-Ho Choi for their
active role in the development of the meeting companion app MeetCues; and Mark
Clougherty, Sean Kennedy, Michael Eggleston, and Marcus Weldon for their
guidance during the development. We also thank Nigel Oseland for sharing his
research at the intersection of environmental psychology and workplace
strategy.

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