About

András Gyenis is an Assistant Professor in the Department of Electrical, Computer & Energy Engineering at the University of Colorado Boulder. He received his PhD in physics from Princeton University in 2016, where he investigated the surface and bulk properties of unconventional superconductors, strongly correlated electronic systems, and topological materials using ultra-low temperature scanning tunneling microscopy. Following his PhD, he continued as a postdoctoral researcher at Princeton, focusing on the design, fabrication, and measurement of superconducting quantum circuits. Between 2020 and 2021, he extended his research to semiconductor-based quantum devices at the Niels Bohr Institute at the University of Copenhagen as a visiting assistant professor. His research program at CU Boulder aims to realize hybrid superconducting–semiconducting quantum devices that harness intrinsic protection to extend the lifetime of quantum processors.

Research topics

• Physics
• Condensed matter physics
• Materials science
• Quantum mechanics
• Computer science

Selected publications

• Controlled Parity of Cooper Pair Tunneling in a Hybrid Superconducting Qubit

  arXiv (Cornell University) · 2026-01-16

  preprintOpen access

  Superconducting quantum circuits derive their nonlinearity from the Josephson energy-phase relation. Besides the fundamental $\cosϕ$ term, this relation can also contain higher Fourier harmonics $\cos(kϕ)$ corresponding to correlated tunneling of $k$ Cooper pairs. The parity of the dominant tunneling process, i.e.~whether an odd or even number of Cooper pairs tunnel, results in qualitatively different properties, and controlling this opens up a wide range of applications in superconducting technology. However, access to even-dominated regimes has remained challenging and has so far relied on complex multi-junction or all-hybrid architectures. Here, we demonstrate a simple "harmonic parity qubit" (HPQ); an element that combines two aluminum-oxide tunnel junctions in parallel to a gate-tunable InAs/Al nanowire junction forming a SQUID, and use spectroscopy versus flux to reconstruct its energy-phase relation at 85 gate voltage points. At half flux quantum, the odd harmonics of the Josephson potential can be suppressed by up to two orders of magnitude relative to the even harmonics, producing a double-well potential dominated by even harmonics with minima near $\pmπ/2$. The ability to control harmonic parity enables supercurrent carried by pairs of Cooper pairs and provides a new building block for Fourier engineering in superconducting circuits.

  PublisherDOI

• Revisiting the multi-mode rhombus circuit as a biased-noise qubit

  arXiv (Cornell University) · 2026-05-07

  preprintOpen accessSenior author

  In this work, we revisit the idea of using an interferometer of pairs of Josephson junctions as a protected rhombus qubit. Unlike in the original proposal, where the qubit states are encoded into odd and even parity charge states, here, we intentionally alter the energy of one of the junctions to investigate the soft version of the rhombus qubit. This approach allows us to directly probe the qubit transitions over several GHz and reduce the potential drawbacks of the interferometer-based protection. Away from a half flux quantum external field, the large shunting capacitors of the circuit ensure localized qubit states in different phase valleys, leading to a biased-noise qubit. In the realized circuit, we measure an average $T_1\approx500\,μ$s relaxation time in the biased-noise regime (with a Ramsey dephasing time of $T^{R}_φ\approx90\,$ns), while an average $T_1\approx27\,μ$s relaxation time at frustration (with $T^{R}_φ\approx670\,$ns). Our loss analysis on this multi-mode circuit indicates that at low frequencies, flux noise and quasiparticle tunneling limit the relaxation times, pointing toward the presence of an optimal operating regime of around a few GHz.

  PublisherDOI

• Junction-Intrinsic Dissipation in Hybrid Superconductor-Semiconductor Gatemon Qubits

  arXiv (Cornell University) · 2026-03-31

  articleOpen access

  Superconducting transmon qubits based on hybrid superconductor-semiconductor Josephson junctions (gatemons) offer gate tunability, but their relaxation times remain well below those of state-of-the-art transmons, and the origin of this discrepancy is not fully understood. Here, we co-fabricate gatemons and SIS-junction transmons with nominally identical circuit layouts, gate dielectrics, and control lines, so that the Josephson element is the only intentional distinction. Across multiple chips, transmons in this architecture reach relaxation times in the tens of microseconds, whereas gatemons saturate in the few-microsecond range. Using the transmons as on-chip references, we construct a loss budget including Purcell decay, spontaneous emission through the control line, and internal dielectric loss, and find that the corresponding T1 limits exceed all measured gatemon values by more than an order of magnitude. Temperature-dependent T1 measurements follow a common quasiparticle-activation model and yield similar superconducting gaps for S-Sm-S and SIS junctions, indicating that the reduced gatemon coherence is dominated by additional temperature-independent, junction-intrinsic dissipation.

  PublisherOA PDF

• Controlled Parity of Cooper Pair Tunneling in a Hybrid Superconducting Qubit

  ArXiv.org · 2026-01-16

  articleOpen access

  Superconducting quantum circuits derive their nonlinearity from the Josephson energy-phase relation. Besides the fundamental $\cosϕ$ term, this relation can also contain higher Fourier harmonics $\cos(kϕ)$ corresponding to correlated tunneling of $k$ Cooper pairs. The parity of the dominant tunneling process, i.e.~whether an odd or even number of Cooper pairs tunnel, results in qualitatively different properties, and controlling this opens up a wide range of applications in superconducting technology. However, access to even-dominated regimes has remained challenging and has so far relied on complex multi-junction or all-hybrid architectures. Here, we demonstrate a simple "harmonic parity qubit" (HPQ); an element that combines two aluminum-oxide tunnel junctions in parallel to a gate-tunable InAs/Al nanowire junction forming a SQUID, and use spectroscopy versus flux to reconstruct its energy-phase relation at 85 gate voltage points. At half flux quantum, the odd harmonics of the Josephson potential can be suppressed by up to two orders of magnitude relative to the even harmonics, producing a double-well potential dominated by even harmonics with minima near $\pmπ/2$. The ability to control harmonic parity enables supercurrent carried by pairs of Cooper pairs and provides a new building block for Fourier engineering in superconducting circuits.

  PublisherOA PDF

• Revisiting the multi-mode rhombus circuit as a biased-noise qubit

  ArXiv.org · 2026-05-07

  articleOpen accessSenior author

  In this work, we revisit the idea of using an interferometer of pairs of Josephson junctions as a protected rhombus qubit. Unlike in the original proposal, where the qubit states are encoded into odd and even parity charge states, here, we intentionally alter the energy of one of the junctions to investigate the soft version of the rhombus qubit. This approach allows us to directly probe the qubit transitions over several GHz and reduce the potential drawbacks of the interferometer-based protection. Away from a half flux quantum external field, the large shunting capacitors of the circuit ensure localized qubit states in different phase valleys, leading to a biased-noise qubit. In the realized circuit, we measure an average $T_1\approx500\,μ$s relaxation time in the biased-noise regime (with a Ramsey dephasing time of $T^{R}_φ\approx90\,$ns), while an average $T_1\approx27\,μ$s relaxation time at frustration (with $T^{R}_φ\approx670\,$ns). Our loss analysis on this multi-mode circuit indicates that at low frequencies, flux noise and quasiparticle tunneling limit the relaxation times, pointing toward the presence of an optimal operating regime of around a few GHz.

  PublisherOA PDF

• Localized quasiparticles in a fluxonium with quasi-two-dimensional amorphous kinetic inductors

  Nature Communications · 2026-02-21 · 1 citations

  articleOpen accessSenior authorCorresponding

  Disordered superconducting materials with high kinetic inductance are an important resource for generating nonlinearity in quantum circuits and creating high-impedance environments. In thin films fabricated from these materials, the combination of disorder and low effective dimensionality leads to increased order parameter fluctuations and enhanced kinetic inductance values. Among the challenges of harnessing these compounds in coherent devices are their proximity to the superconductor-insulator phase transition and the two-level systems located in the disordered structure. Here, we fabricate tungsten silicide wires from quasi-two-dimensional films and embed them into microwave resonators and fluxonium qubits, where the kinetic inductance provides the inductive part of the circuits. In this work, we study the dependence of loss on the frequency, disorder, and geometry of the devices, and find that the loss increases with the level of disorder and is dominated by the localized quasiparticles trapped in the spatial variations of the superconducting gap. High kinetic inductance materials are widely used in superconducting circuits, yet their loss mechanisms are not fully understood. Here the authors study quantum circuits incorporating nanowires made of quasi-2D disordered superconductor WSi and identify localized quasiparticles as the dominant source of loss.

  PublisherDOI

• WSi weak link element with a non-sinusoidal current-phase relation

  arXiv (Cornell University) · 2026-05-20

  preprintOpen accessSenior author

  Nonlinearity is an essential ingredient for encoding quantum states with non-uniform energy spacing, implementing coherent quantum gates, reading out qubits, amplifying, and mixing electromagnetic signals. In this work, we demonstrate the nonlinear behavior of a constriction fabricated from an amorphous, high-kinetic inductance material, tungsten silicide, embedded in a three-dimensional RF-SQUID. We find that the results are consistent with the weak link behaving as a Josephson junction with a sawtooth-like current-phase relation or a quantum phase slip element. Finally, we measure relaxation times of the metastable, persistent-current states trapped in the local minima of the potential.

  PublisherDOI

• Junction-Intrinsic Dissipation in Hybrid Superconductor-Semiconductor Gatemon Qubits

  arXiv (Cornell University) · 2026-03-31

  preprintOpen access

  Superconducting transmon qubits based on hybrid superconductor-semiconductor Josephson junctions (gatemons) offer gate tunability, but their relaxation times remain well below those of state-of-the-art transmons, and the origin of this discrepancy is not fully understood. Here, we co-fabricate gatemons and SIS-junction transmons with nominally identical circuit layouts, gate dielectrics, and control lines, so that the Josephson element is the only intentional distinction. Across multiple chips, transmons in this architecture reach relaxation times in the tens of microseconds, whereas gatemons saturate in the few-microsecond range. Using the transmons as on-chip references, we construct a loss budget including Purcell decay, spontaneous emission through the control line, and internal dielectric loss, and find that the corresponding T1 limits exceed all measured gatemon values by more than an order of magnitude. Temperature-dependent T1 measurements follow a common quasiparticle-activation model and yield similar superconducting gaps for S-Sm-S and SIS junctions, indicating that the reduced gatemon coherence is dominated by additional temperature-independent, junction-intrinsic dissipation.

  PublisherDOI

• WSi weak link element with a non-sinusoidal current-phase relation

  ArXiv.org · 2026-05-20

  articleOpen accessSenior author

  Nonlinearity is an essential ingredient for encoding quantum states with non-uniform energy spacing, implementing coherent quantum gates, reading out qubits, amplifying, and mixing electromagnetic signals. In this work, we demonstrate the nonlinear behavior of a constriction fabricated from an amorphous, high-kinetic inductance material, tungsten silicide, embedded in a three-dimensional RF-SQUID. We find that the results are consistent with the weak link behaving as a Josephson junction with a sawtooth-like current-phase relation or a quantum phase slip element. Finally, we measure relaxation times of the metastable, persistent-current states trapped in the local minima of the potential.

  PublisherOA PDF

• Gatemon qubit revisited for improved reliability and stability

  Physical Review Applied · 2025-09-30 · 2 citations

  article

  The development of quantum circuits based on hybrid superconductor-semiconductor Josephson junctions holds promise for exploring their mesoscopic physics and for building innovative superconducting devices. The gate-tunable superconducting transmon qubit (gatemon) is the paradigmatic example of such a superconducting circuit; however, gatemons typically suffer from unstable and hysteretic qubit frequencies with respect to the applied gate voltage and reduced coherence times compared to conventional transmons fabricated from aluminum-oxide-based Josephson junctions. Here, we develop methods for characterizing these challenges in gatemons and deploy these methods to compare the impact of shunt-capacitor designs on gatemon performance. Our results indicate a strong frequency- and design-dependent behavior of the qubit stability, hysteresis, and dephasing times. Moreover, we achieve highly reliable tuning of the qubit frequency with 1-MHz precision over a range of several gigahertz, along with improved stability in grounded gatemons compared to gatemons with a floating capacitor design.

  PublisherDOI

Frequent coauthors

• Ali Yazdani

  25 shared

• Andrew Houck

  23 shared

• Alexandre Blais

  16 shared

• Jens Koch

  16 shared

• R. J. Cava

  15 shared

• Agustín Di Paolo

  14 shared

• Pranav Mundada

  13 shared

• Benjamin E. Feldman

  Stanford University

  11 shared

Labs

• Gyenis LabPI

  Design of new superconducting circuit components for protected qubits from disordered superconductors.

Education

• Ph.D., Physics

  Princeton University

  2016

• M.S., Experimental Condensed Matter Physics

  Budapest University of Technology

• B.S., Experimental Condensed Matter Physics

  Budapest University of Technology