News
Malick Sere receives the 2026 Frederick C. Hennie III Teaching Award
QNN grad student Malick Sere was awarded the 2026 Frederick C. Hennie III Teaching Award in recognition of his outstanding contributions to teaching within the EECS department. He worked with our own Donnie Keathley as a TA in the Spring semester for 6.2410 – Laboratory in Quantum Systems Engineering: Quantum Engineering. Platforms. Throughout that class, many students mentioned how they appreciated his guidance and instruction in the class.
For more on Frederick C. Hennie III, for whom this award is named, see this EECS memorial article. Unsurprisingly, he also won an award for his work in teaching while a graduate student.
New Publication: Field-resolved observation of exciton coherence in a van der Waals magnet
A new publication written from the group using nanoantenna field-sampling techniques to observe femtosecond-scale coherent exciton dynamics in CrSBr was recently published in Nature Materials.
Matthew Yeung, Alexander von Hoegen, Emil Viñas Boström, Fangzhou Zhao, Felix Ritzkowsky, Jack B. Maier, Gian Luca Dolso, Christian Heide, Daniel G. Chica, Xavier Roy, Karl K. Berggren, Angel Rubio, Philip D. Keathley, and Nuh Gedik. “Field-resolved observation of exciton coherence in a van der Waals magnet.” Nat. Mater., p. 1-7, May 2026
The emergence of coherence among electronic quasiparticles underlies collective quantum phenomena from superconductivity to superradiance. In semiconductors, exciton coherence is generally thought to decay rapidly due to scattering and dephasing, limiting its persistence on ultrafast timescales. Here we demonstrate a light-field-driven mechanism that creates and stabilizes exciton coherence in the layered antiferromagnet CrSBr. We directly record the coherent optical field emitted by excitons and track in real time how a deterministic phase, imprinted by the excitation laser, drives incoherent excitons to synchronize into a collective state. This ensemble remains phase coherent for more than 2 ps, whereas its resonance energy undergoes an ultrafast modulation mediated by spin and lattice interactions. The time-resolved field evolution indicates that the multiple peaks seen in conventional spectra originate from a single excitonic resonance subject to dynamic energy modulation. Our findings establish optical phase imprinting as a mechanism to control and sustain collective order in semiconducting magnets, bridging light-driven dynamics with excitonic and magnetic correlations in layered quantum materials.
QNN Newsletter from IAP 2026
Dear QNN Group Members, Alums and Affiliates,
Hope everyone is enjoying the start to Spring! We are excited to share updates from the QNN group over the last months.
It has been a while since our last newsletter, so a lot of activity to report. In particular we want to highlight that Dip Joti Paul received the 2026 Claude Shannon Award from RLE, and Adina Bechhofer the 2026 Samsung Semiconductor Fellowship from EECS. Also, last November we held our annual group retreat at Endicott house and have included a picture from the event. As usual, we provide a quick summary of comings and goings, awards, research activity and events below.
Best regards,
Karl and Donnie
Comings and Goings
The last few months we’ve welcomed the following new group members:
- Dong min Kim, Visiting Scientist
- Zhenyang Xiao, Postdoctoral Associate
- Eileen Xiu, UROP
- Jaden McKee, UROP
- Berkan Tarak, UROP
The following members have now left and become alumni group members:
- Josh Piety, UROP, graduated!
- Hanson Nguyen, Undergrad researcher, MSRP
- Giorgia Ciuffarella, Polytechnic of Turin & École Polytechnique Fédérale de Lausanne, graduated!
- Gabriel LeGuay, Federal Polytechnique School of Zurich, graduated!
- Owen Medeiros, working as a Superconducting Electronics Architect at MIT Lincoln Lab
Awards
- Dip Joti Paul has received the 2026 Claude E. Shannon Award!
- Adina Bechhoffer has received the Samsung Semiconductor Fellowship!
Theses!
G. Ciuffarella, “Infrared-Enhanced Electron Emission from Nanoantennas for Optical Detection,” Ecole Polytechnique Federale de Lausanne and Massachusetts Institute of Technology, 2025.
G. Le Guay, “Reconfigurable superconducting logic gate: From photon-driven operation to electro-optic modulation,” Master’s Thesis, Swiss Federal Institute of Technology, Zurich and Massachusetts Institute of Technology, 2025.
Publications (6/1/25-1/31/26)
R. A. Foster, S. Kandeh, O. Medeiros, A. Simon, M. Castellani, and K. K. Berggren, “Time-tagging data acquisition system for testing superconducting electronics based on an RFSoC and custom analog frontend,” J. Inst., vol. 20, no. 09, p. P09018, Sep. 2025, doi: 10.1088/1748-0221/20/09/P09018.
R. Jing et al., “Bolometric Superconducting Optical Nanoscopy (BOSON),” Phys. Rev. X, vol. 15, no. 3, p. 031027, Jul. 2025, doi: 10.1103/f13d-dpdn.
V. Karam et al., “Parameter extraction for a SPICE model of an hTron superconducting thermal switch,” Phys. Rev. Appl., vol. 24, no. 2, p. 024020, Aug. 2025, doi: http://dx.doi.org/10.1103/jdzc-7l2x.
O. Medeiros et al., “A scalable superconducting nanowire memory array with row–column addressing,” Nat Electron, pp. 1–9, Jan. 2026, doi: 10.1038/s41928-025-01512-0.
H. Nguyen, A. Simon, R. A. Foster, and K. K. Berggren, “Modeling electrothermal feedback of superconducting nanowire single photon detectors in SPICE,” IEEE Trans. Appl. Supercond., vol. 35, no. 9, pp. 1–5, Dec. 2025, doi: 10.1109/TASC.2025.3625542.
D. J. Paul, T. X. Zhou, and K. K. Berggren, “Determination of mid-infrared refractive indices of superconducting thin films using Fourier transform infrared spectroscopy,” Appl. Phys. Lett., vol. 126, no. 25, p. 252601, Jun. 2025, doi: 10.1063/5.0268308.
D. J. Paul, T. X. Zhou, and K. K. Berggren, “Photolithography-compatible three-terminal superconducting switch for driving CMOS loads,” Phys. Rev. Appl., vol. 24, no. 2, p. 024060, Aug. 2025, doi: 10.1103/261b-37xx.
F. Ritzkowsky, M. Yeung, G. L. Dolso, L.-T. Chou, and P. D. Keathley, “High-repetition rate, CEP-stable shortwave infrared source with two-cycle pulses for field-resolved spectroscopy,” J. Opt. Soc. Am. B, JOSAB, vol. 43, no. 1, pp. 207–212, Jan. 2026, doi: 10.1364/JOSAB.580422.
Z. Scherübl et al., “Multimode Operation of a Superconducting Nanowire Switch in the Nanosecond Regime,” ACS Nano, vol. 19, no. 32, pp. 29207–29215, Aug. 2025, doi: 10.1021/acsnano.5c03718.
A. Simon et al., “Ab initio modeling of nonequilibrium dynamics in superconducting detectors and qubits,” Phys. Rev. B, vol. 112, no. 17, p. 174512, Nov. 2025, doi: 10.1103/3m2k-mzr6.
J. W. Simonaitis, J. A. Alongi, B. Slayton, W. P. Putnam, K. K. Berggren, and P. D. Keathley, “Electron energy loss spectroscopy of two-dimensional materials in a scanning electron microscope,” Phys. Rev. B, vol. 112, no. 23, p. 235421, Dec. 2025, doi: 10.1103/tdfh-1ppp.<
Conferences & Proceedings (6/1/25-1/31/26)
K. K. Berggren, “Superconducting Nanowire Single-Photon Detectors for Quantum Sensing: From Photon-Number Resolution to Dark-Matter Detection,” presented at the Munich Conference on Quantum Science & Technology, Kufstein, Austria, Jun. 05, 2025. [Online]. Available: https://www.youtube.com/watch?v=-DgP-F5uu1A
K. K. Berggren, “Superconducting Nanostrip Single-Photon Detectors,” presented at the Low-Temperature Quantum Detectors 2025, Helsinki, Finland, Aug. 06, 2025.
K. K. Berggren, “Superconducting Nanowire Single-Photon Detectors,” presented at the Optica Incubator on Cryogenic Integrated Photonics for Classical and Quantum Systems, Washington, DC, Sep. 11, 2025.
K. K. Berggren, “Superconducting Cryotron-Like Electronic Devices and Circuits,” presented at the EUCAS 2025, Porto, Portugal, Sep. 23, 2025.
K. K. Berggren, “Superconducting Nanowire Single-Photon Detectors for Quantum Sensing: From Photon-Number Resolution to Dark-Matter Detection,” presented at the Q-FARM Seminar, Stanford University, California., Oct. 01, 2025.
K. K. Berggren, “Superconducting Detectors and Electronics for Quantum Sensing and Applications in Space,” presented at the Detector Technology Seminar, NASA Goddard Space Flight Center, Virtual, Jan. 14, 2026.
L. C. Blackburn, “SuperLoop: Architecture Modeling for Superconducting AI Accelerators,” presented at the EUCAS 2025, Porto, Portugal, Sep. 22, 2025.
M. Castellani, “Superconducting Nanowire Electronic Devices and Circuits,” presented at the International Conference on Superconductor Materials and Metama- terials for Quantum Hardware: Devices, Circuits, and Systems, Glasgow, UK, Nov. 2025.
R. A. Foster, “Fast numerical methods for the Usadel equation,” presented at the EUCAS 2025, Porto, Portugal, Sep. 22, 2025.
R. A. Foster, “Fast numerical methods for the Usadel equation,” TU Graz, Oct. 15, 2025.
F. Incalza, “Superconducting Nanowire Single-Photon Detectors Fabricated on Epitaxial NbN Thin Films Grown by Sputtering,” presented at the European Conference on Applied Superconductivity (EUCAS 2025), Munich, Germany, Sep. 2025.
Reed A. Foster, “Scalable superconducting multilayer process for digital imager readout with nanocryotrons,” presented at the MARC, Brettn Woods, NH, Jan. 27, 2026.
A. Simon, “Ab initio modeling of superconducting devices,” presented at the EUCAS, Porto, Portugal, Aug. 14, 2025.
A. Simon, “Ab initio modeling of superconducting devices,” TU Graz, Oct. 15, 2025.
F. Ritzkowsky, M. Yeung, G. L. Dolso, L.-T. Chuo, and P. D. Keathley, “High-Repetition Rate 2.3-Cycle Shortwave-Infrared Source for Next-Generation Field-Resolved Spectroscopy,” in 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Jun. 2025. doi: 10.1109/CLEO/Europe-EQEC65582.2025.11109943.
A. Bechhofer, J. Simonaitis, F. Ritzkowsky, L. Daniel, K. K. Berggren, and P. D. Keathley, “Exploring Parasitics and Coupling between Optically Driven Nanoantennas and Interconnects in Petahertz Electronic Circuits,” in 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, Germany, Jun. 2025. doi: 10.1109/CLEO/Europe-EQEC65582.2025.11109477.
P. D. Keathley, “Nanoscale Petahertz-Electronics for Field-Resolved Spectroscopy,” in 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), Munich, Germany: IEEE, Jun. 2025. doi: 10.1109/CLEO/Europe-EQEC65582.2025.11109586.
Preprints (6/1/25-1/31/26)
F. Incalza et al., “Fast-Recovery Epitaxial NbN Superconducting Nanowire Single-Photon Detectors with Saturated Efficiency at 1550 nm in Liquid Helium,” Dec. 19, 2025, arXiv:2512.18063. doi: 10.48550/arXiv.2512.18063.
From left to right: Gian Luca Dolsa, Karl Berggren, Joey Alongi, Reed Foster, Alejandro Simon, Malick Sere, DJ Paul, Emma Batson, Gabriel La Guay, Ari Willner, Francesca Incalza, Donnie Keathley, Evan Golden, Dorothy Fleischer, Ben Mazur, Daniel Graham, Matteo Casellani, and Dong-min Kim.
New Publication: Electron energy loss spectroscopy of two-dimensional materials in a scanning electron microscope
A new publication written by the group on the characterization of 2D materials in a scanning electron microscope was published in Physical Review B.
John W. Simonaitis, Joseph A. Alongi, Benjamin Slayton, William P. Putnam, Karl K. Berggren, and Phillip D. Keathley, “Electron energy loss spectroscopy of two-dimensional materials in a scanning electron microscope,” Phys. Rev. B, 112, 23, p. 235421, December 19, 2025. | ArXiV
This work demonstrates electron energy loss spectroscopy of 2D materials in the 1–20 keV incident electron energy range, observing 50 times stronger electron-matter scattering relative to 125 keV microscopes. We observe that the universal curve relating beam energy to scattering holds for the transition from bulk graphite to graphene, albeit with a scale factor. We calculate that optimal coupling for most 2D materials and optical nanostructures falls in this range, concluding that spectroscopy of such systems could greatly benefit from use of this energy regime.
New Publication on High-speed testing of superconducting electronics
A new publication written by the group on custom sensing equipment was recently published in the Journal of Instrumentation.
Abstract
Novel electronic devices can often be operated in a plethora of ways, which makes testing circuits comprised of them difficult. Often, no single tool can simultaneously analyze the operating margins, maximum speed, and failure modes of a circuit, particularly when the intended behavior of subcomponents of the circuit is not standardized. This work demonstrates a cost-effective time-domain data acquisition system for electronic circuits that enables more intricate verification techniques than are practical with conventional experimental setups. We use high-speed digital-to-analog converters and real-time multi-gigasample-per-second waveform processing to push experimental circuits beyond their maximum operating speed. Our custom time-tagging data capture firmware reduces memory requirements and can be used to determine when errors occur. The firmware is combined with a thermal-noise-limited analog frontend with 50 dB of dynamic range. Compared to currently available commercial test equipment that is seven times more expensive, this data acquisition system was able to operate a superconducting shift register at a nearly three-times-higher clock frequency (200 MHz vs. 80 MHz).