About

Andrew Houck is a Professor of Electrical and Computer Engineering at Princeton University, with a focus on quantum mechanics as it relates to electronics. His research centers on fully quantum mechanical integrated circuits, combining principles of quantum mechanics, superconducting electronics, microwave circuits, quantum optics, and low-temperature measurement. A key component of his work involves circuit quantum electrodynamics (cQED), which includes superconducting qubits coupled to on-chip microwave resonators, enabling experiments in quantum computing and non-linear optics. His research aims to develop robust, scalable quantum architectures by addressing issues such as decoherence and circuit complexity, and explores quantum and non-linear optics in microwave devices. Houck's work has contributed to understanding how quantum information can be stored, manipulated, and transmitted in integrated circuits, advancing the field of quantum computing and quantum optics. He has received numerous awards, including the Presidential Early Career Award for Scientists and Engineers, NSF Early Career Award, and a Sloan Research Fellowship, among others.

Research topics

• Quantum mechanics
• Computer Science
• Physics
• Data science
• History
• Theoretical physics
• Library science

Selected publications

• Quantifying surface losses in superconducting aluminum microwave resonators

  ArXiv.org · 2026-03-13

  articleOpen access

  The recent realization of millisecond-scale coherence with tantalum-on-silicon transmon qubits showed that depositing the Al/AlOx/Al Josephson junction in a high purity, ultrahigh vacuum environment was critical for achieving lifetime-limited coherence, motivating careful examination of the aluminum surface two-level system (TLS) bath. Here, we measure the microwave absorption arising from surface TLSs in superconducting aluminum resonators, following methodology developed for tantalum resonators. We vary film and surface properties and correlate microwave measurements with materials characterization. We find that the lifetimes of superconducting aluminum resonators are primarily limited by surface losses associated with TLSs in the 2.7 nm-thick native AlOx. Treatment with 49% HF removes surface AlOx completely; however, rapid oxide regrowth limits improvements in surface loss and long term device stability. Using these measurements we estimate that TLSs in aluminum interfaces contribute around 27% of the relaxation rate of state-of-the-art tantalum-on-silicon qubits that incorporate aluminum-based Josephson junctions.

  PublisherOA PDF

• Quantifying surface losses in superconducting aluminum microwave resonators

  arXiv (Cornell University) · 2026-03-13

  preprintOpen access

  The recent realization of millisecond-scale coherence with tantalum-on-silicon transmon qubits showed that depositing the Al/AlOx/Al Josephson junction in a high purity, ultrahigh vacuum environment was critical for achieving lifetime-limited coherence, motivating careful examination of the aluminum surface two-level system (TLS) bath. Here, we measure the microwave absorption arising from surface TLSs in superconducting aluminum resonators, following methodology developed for tantalum resonators. We vary film and surface properties and correlate microwave measurements with materials characterization. We find that the lifetimes of superconducting aluminum resonators are primarily limited by surface losses associated with TLSs in the 2.7 nm-thick native AlOx. Treatment with 49% HF removes surface AlOx completely; however, rapid oxide regrowth limits improvements in surface loss and long term device stability. Using these measurements we estimate that TLSs in aluminum interfaces contribute around 27% of the relaxation rate of state-of-the-art tantalum-on-silicon qubits that incorporate aluminum-based Josephson junctions.

  PublisherDOI

• Beta Tantalum Transmon Qubits with Quality Factors Approaching 10 Million

  arXiv (Cornell University) · 2026-03-13

  preprintOpen access

  Tantalum-based transmon qubits are a promising platform for building large-scale quantum processors. So far, these qubits have been made from tantalum films grown exclusively in the alpha phase (α-Ta). The beta phase of tantalum (\{beta}-Ta) readily nucleates at room temperature, making it attractive for scalable qubit fabrication. However, \{beta}-Ta is widely believed to be detrimental to qubit performance because it has a lower superconducting critical temperature than α-Ta. We challenge this prevailing belief by fabricating low-loss transmon qubits from \{beta}-Ta films on sapphire. Across 11 qubits, the mean time-averaged quality factor is (5.6 +/- 2.3) x 10^6, with the best qubit recording a time-averaged quality factor of (10.1 +/- 1.3) x 10^6. Resonator studies demonstrate that the dominant microwave loss channel is surface two-level systems, with the surface loss contribution for \{beta}-Ta being about twice that of α-Ta. \{beta}-Ta films exhibit significant kinetic inductance, consistent with an estimated magnetic penetration depth of (1.78 +/- 0.02) μm. This work establishes \{beta}-Ta on sapphire as a material platform for realizing low-loss transmon qubits and other superconducting devices such as compact resonators, kinetic inductance detectors, and quasiparticle traps.

  PublisherDOI

• Tantalum alloy–based resonators for quantum information systems

  Proceedings of the National Academy of Sciences · 2026-01-29

  articleOpen access

  Utilizing tantalum (Ta) in superconducting circuits has led to significant improvements, such as high qubit lifetime (T 1 ) and quality factors in both qubits and resonators, suggesting that material optimization plays an important role in the development of superconducting circuits. Thus we here explore superconducting gap engineering in Ta-based devices as a powerful strategy for expanding the range of suitable host materials. By alloying 20 atomic percent (at.%) hafnium into Ta thin films, we achieve a superconducting transition temperature (T c ) of 6.09 K as observed in direct current (DC) transport measurements, reflecting an increase in the superconducting gap. We systematically vary deposition conditions to control film orientation and transport properties of Ta-Hf alloy thin films. We then confirm the enhancement in T c via microwave measurements at millikelvin temperatures. We verify the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>∼</mml:mo> </mml:math> 40 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>%</mml:mo> </mml:math> increase in T c relative to bare Ta devices, while the loss contributions from two-level systems and quasi-particles remain unchanged in the low temperature regime. These findings emphasize the promise of material engineering in superconducting circuits and point to many potential material candidates for further exploration.

  PublisherDOI

• Vortex motion induced losses in tantalum resonators

  Physical review. B./Physical review. B · 2026-01-07

  article
  PublisherDOI

• Beta Tantalum Transmon Qubits with Quality Factors Approaching 10 Million

  arXiv (Cornell University) · 2026-03-13

  articleOpen access

  Tantalum-based transmon qubits are a promising platform for building large-scale quantum processors. So far, these qubits have been made from tantalum films grown exclusively in the alpha phase (α-Ta). The beta phase of tantalum (\{beta}-Ta) readily nucleates at room temperature, making it attractive for scalable qubit fabrication. However, \{beta}-Ta is widely believed to be detrimental to qubit performance because it has a lower superconducting critical temperature than α-Ta. We challenge this prevailing belief by fabricating low-loss transmon qubits from \{beta}-Ta films on sapphire. Across 11 qubits, the mean time-averaged quality factor is (5.6 +/- 2.3) x 10^6, with the best qubit recording a time-averaged quality factor of (10.1 +/- 1.3) x 10^6. Resonator studies demonstrate that the dominant microwave loss channel is surface two-level systems, with the surface loss contribution for \{beta}-Ta being about twice that of α-Ta. \{beta}-Ta films exhibit significant kinetic inductance, consistent with an estimated magnetic penetration depth of (1.78 +/- 0.02) μm. This work establishes \{beta}-Ta on sapphire as a material platform for realizing low-loss transmon qubits and other superconducting devices such as compact resonators, kinetic inductance detectors, and quasiparticle traps.

  PublisherOA PDF

• Open-Motion: an open source high sensitivity low cost blood flowmeter platform

  2025-03-19 · 1 citations

  article

  Open-Motion is an open source diagnostic platform intended to help researchers study tissue blood flow and blood volume in laboratory, pre-clinical, and clinical research settings. The platform is designed to be flexible and re-programmable so that a wide variety of tissue types can be explored, while also enabling researchers to configure constrained operation modes so that trained operators can use the system to complete specified workflows, and entities seeking regulatory approval for specific indications can use realizations of the platform in commercial products. The platform utilizes a pulsed long coherence length laser with a pulse width tuned to maximize the platform’s sensitivity to changes in blood flow. By performing most of the computation on individual cameras instead of in a central computer, an arbitrary number of cameras can be used, making the platform configurable for a wide number of applications.

  PublisherDOI

• Sub-resonant wideband superconducting Purcell filters

  ArXiv.org · 2025-03-13

  preprintOpen accessSenior author

  In superconducting quantum devices, Purcell filters protect qubit information from decaying into external lines by reducing external coupling at qubit frequencies while maintaining it at readout frequencies. Here, we introduce and demonstrate a novel Purcell filter design that places the readout resonator frequencies in a "linewidth plateau" below the filter's first resonant mode. This approach, based on direct admittance engineering, can simultaneously achieve strong qubit protection and nearly constant external coupling across a wide readout bandwidth, addressing the traditional tradeoff between these properties. We first present a lumped-element analysis of our filters. We then experimentally demonstrate a compact on-chip linewidth-plateau filter, coupled to four resonators across its approximately 1 GHz readout band. We compare the measured linewidths to numerical predictions, and show how the filter protects a frequency-tunable transmon qubit from external decay. We envision that our flexible design paradigm will aid in efforts to create multiplexed readout architectures for superconducting quantum circuits, with well-controlled external couplings.

  PublisherOA PDFDOI

• Eliminating Surface Oxides of Superconducting Circuits with Noble Metal Encapsulation

  Physical Review Letters · 2025-03-06 · 22 citations

  articleOpen access

  The lifetime of superconducting qubits is limited by dielectric loss, and a major source of dielectric loss is the native oxide present at the surface of the superconducting metal. Specifically, tantalum-based superconducting qubits have been demonstrated with record lifetimes, but a major source of loss is the presence of two-level systems in the surface tantalum oxide. Here, we demonstrate a strategy for avoiding oxide formation by encapsulating the tantalum with noble metals that do not form native oxide. By depositing a few nanometers of Au or AuPd alloy before breaking vacuum, we completely suppress tantalum oxide formation. Microwave loss measurements of superconducting resonators reveal that the noble metal is proximitized, with a superconducting gap over 80% of the bare tantalum at thicknesses where the oxide is fully suppressed. Our findings suggest that losses in resonators fabricated by subtractive etching are dominated by oxides on the sidewalls, pointing to total surface encapsulation by additive fabrication as a promising strategy for eliminating surface oxide two-level system loss in superconducting qubits.

  PublisherOA PDFDOI

• Vortex Motion Induced Losses in Tantalum Resonators

  ArXiv.org · 2025-03-05

  preprintOpen access

  Tantalum (Ta) based superconducting circuits have been demonstrated to enable record qubit coherence times and quality factors, motivating a careful study of the microscopic origin of the remaining losses that limit their performance. We have recently shown that the losses in Ta-based resonators are dominated by two-level systems (TLSs) at low microwave powers and millikelvin temperatures. We also observe that some devices exhibit loss that is exponentially activated at a lower temperature inconsistent with the superconducting critical temperature (Tc) of the constituent film. Specifically, dc resistivity measurements show a Tc of over 4 K, while microwave measurements of resonators fabricated from these films show losses that increase exponentially with temperature with an activation energy as low as 0.3 K. Here, we present a comparative study of the structural and thermodynamic properties of Ta-based resonators and identify vortex motion-induced loss as the source of thermally activated microwave loss. Through careful magnetoresistance and x-ray diffraction measurements, we observe that the increased loss occurs for films that are in the clean limit, where the superconducting coherence length is shorter than the mean free path. Vortex motion-induced losses are suppressed for films in the dirty limit, which show evidence of structural defects that can pin vortices. We verify this hypothesis by explicitly pinning vortices via patterning and find that we can suppress the loss by microfabrication.

  PublisherOA PDF

Recent grants

• Many-Body Quantum Optics and Light-Matter Interactions in Superconducting Circuits

  NSF · $580k · 2016–2022

• CAREER: Strongly Correlated Photons in Microwave Cavities and Coupled Cavity Arrays

  NSF · $550k · 2010–2016

Frequent coauthors

• Jens Koch

  58 shared

• David Schuster

  Electronics for Imaging (United States)

  38 shared

• Jay Gambetta

  IBM (United States)

  35 shared

• Alexandre Blais

  33 shared

• S. M. Girvin

  Yale University

  29 shared

• Pranav Mundada

  27 shared

• Srikanth Srinivasan

  27 shared

• András Gyenis

  University of Colorado Boulder

  23 shared

Education

• Post-doctorate degree, Applied Physics

  Yale University

  2008

• Ph.D. , Physics

  Harvard University

  2005

• BSE, Electrical Engineering

  Princeton University

  2000

Awards & honors

• Presidential Early Career Award for Scientists and Engineers…
• NSF Early Career Award (2010)
• Packard Fellow (2009)
• Technology Review TR35 (2009)
• Sloan Research Fellowship (2009)