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Decoherence of surface phonons in a quantum acoustic system
Authors:
Camryn Undershute,
Joseph M. Kitzman,
Camille A. Mikolas,
Johannes Pollanen
Abstract:
Phononic resonators are becoming increasingly important in quantum information science, both for applications in quantum computing, communication and sensing, as well as in experiments investigating fundamental physics. Here, we study the decoherence of phonons confined in a surface acoustic wave (SAW) resonator strongly coupled ($g/2π\approx 9$ MHz) to a superconducting transmon qubit. By compari…
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Phononic resonators are becoming increasingly important in quantum information science, both for applications in quantum computing, communication and sensing, as well as in experiments investigating fundamental physics. Here, we study the decoherence of phonons confined in a surface acoustic wave (SAW) resonator strongly coupled ($g/2π\approx 9$ MHz) to a superconducting transmon qubit. By comparing experimental data with numerical solutions to the Markovian master equation, we report a surface phononic energy decay rate of $κ_1/2π=480$ kHz and a pure dephasing rate of $κ_φ/2π=180$ kHz. These rates are in good agreement with the level of decoherence we extract from qubit-assisted spectroscopic measurements of the SAW resonator. We additionally find that the timescales over which coherent driven dynamics and decoherence occur are comparable, highlighting the need to model the composite device as an open quantum system. We discuss possible sources of decoherence in SAW-based quantum acoustic devices and the application of these devices in future quantum acoustic dissipation engineering experiments. The decoherence characterization techniques we employ are broadly applicable for investigating and benchmarking the effects of loss and dephasing on mechanical resonators in the quantum regime.
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Submitted 19 February, 2025; v1 submitted 3 October, 2024;
originally announced October 2024.
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Free-space coupling and characterization of transverse bulk phonon modes in lithium niobate in a quantum acoustic device
Authors:
J. M. Kitzman,
J. R. Lane,
C. Undershute,
M. Drimmer,
A. J. Schleusner,
N. R. Beysengulov,
C. A. Mikolas,
J. Pollanen
Abstract:
Transverse bulk phonons in a multimode integrated quantum acoustic device are excited and characterized via their free-space coupling to a three-dimensional (3D) microwave cavity. These bulk acoustic modes are defined by the geometry of the Y-cut lithium niobate substrate in which they reside and couple to the cavity electric field via a large dipole antenna, with an interaction strength on the or…
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Transverse bulk phonons in a multimode integrated quantum acoustic device are excited and characterized via their free-space coupling to a three-dimensional (3D) microwave cavity. These bulk acoustic modes are defined by the geometry of the Y-cut lithium niobate substrate in which they reside and couple to the cavity electric field via a large dipole antenna, with an interaction strength on the order of the cavity line-width. Using finite element modeling (FEM) we determine that the bulk phonons excited by the cavity field have a transverse polarization with a shear velocity matching previously reported values. We demonstrate how the coupling between these transverse acoustic modes and the electric field of the 3D cavity depends on the relative orientation of the device dipole, with a coupling persisting to room temperature. Our study demonstrates the versatility of 3D microwave cavities for mediating contact-less coupling to quantum, and classical, piezoacoustic devices.
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Submitted 2 February, 2024; v1 submitted 1 August, 2023;
originally announced August 2023.
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Quantum acoustic Fano interference of surface phonons
Authors:
J. M. Kitzman,
J. R. Lane,
C. Undershute,
N. R. Beysengulov,
C. A. Mikolas,
K. W. Murch,
J. Pollanen
Abstract:
Quantum acoustic systems, which integrate surface or bulk phonons with superconducting qubits, offer a unique opportunity to investigate phononic $interference$ and $scattering$ processes in the quantum regime. In particular the interaction between a superconducting qubit and a phononic oscillator allows the qubit to sense the oscillator's excitation spectrum and underlying interference effects. H…
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Quantum acoustic systems, which integrate surface or bulk phonons with superconducting qubits, offer a unique opportunity to investigate phononic $interference$ and $scattering$ processes in the quantum regime. In particular the interaction between a superconducting qubit and a phononic oscillator allows the qubit to sense the oscillator's excitation spectrum and underlying interference effects. Here we present measurements revealing Fano interference of a resonantly trapped piezoelectric surface acoustic wave (SAW) mode with a broad continuum of surface phonons in a system consisting of a SAW resonator coupled to a superconducting qubit. The experiments highlight the existence of additional weakly coupled mechanical modes and their influence on the qubit-phonon interaction and underscore the importance of phononic interference in quantum acoustic architectures that have been proposed for quantum information processing applications.
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Submitted 24 July, 2023; v1 submitted 2 February, 2023;
originally announced February 2023.
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Phononic bath engineering of a superconducting qubit
Authors:
J. M. Kitzman,
J. R. Lane,
C. Undershute,
P. M. Harrington,
N. R. Beysengulov,
C. A. Mikolas,
K. W. Murch,
J. Pollanen
Abstract:
Phonons, the ubiquitous quanta of vibrational energy, play a vital role in the performance of quantum technologies. Conversely, unintended coupling to phonons degrades qubit performance and can lead to correlated errors in superconducting qubit systems. Regardless of whether phonons play an enabling or deleterious role, they do not typically admit control over their spectral properties, nor the po…
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Phonons, the ubiquitous quanta of vibrational energy, play a vital role in the performance of quantum technologies. Conversely, unintended coupling to phonons degrades qubit performance and can lead to correlated errors in superconducting qubit systems. Regardless of whether phonons play an enabling or deleterious role, they do not typically admit control over their spectral properties, nor the possibility of engineering their dissipation to be used as a resource. Here we show that coupling a superconducting qubit to a bath of piezoelectric surface acoustic wave phonons enables a novel platform for investigating open quantum systems. By shaping the loss spectrum of the qubit via the bath of lossy surface phonons, we demonstrate preparation and dynamical stabilization of superposition states through the combined effects of drive and dissipation. These experiments highlight the versatility of engineered phononic dissipation and advance the understanding of mechanical losses in superconducting qubit systems.
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Submitted 24 July, 2023; v1 submitted 15 August, 2022;
originally announced August 2022.
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Helium surface fluctuations investigated with superconducting coplanar waveguide resonator
Authors:
N. R. Beysengulov,
C. A. Mikolas,
J. M. Kitzman,
J. R. Lane,
D. Edmunds,
D. G. Rees,
E. A. Henriksen,
S. A. Lyon,
J. Pollanen
Abstract:
Recent experiments on the coupling of the in-plane motional state of electrons floating on the surface of liquid helium to a microwave resonator have revealed the importance of helium surface fluctuations to the coherence of this motion. Here we investigate these surface fluctuations by studying the resonance properties of a superconducting coplanar waveguide (CPW) resonator filled with superfluid…
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Recent experiments on the coupling of the in-plane motional state of electrons floating on the surface of liquid helium to a microwave resonator have revealed the importance of helium surface fluctuations to the coherence of this motion. Here we investigate these surface fluctuations by studying the resonance properties of a superconducting coplanar waveguide (CPW) resonator filled with superfluid helium, where a significant fraction of the resonator's electromagnetic mode volume is coupled to the surface dynamics of the liquid. We present preliminary results on real-time CPW resonator frequency shifts driven by helium fluctuations, which are quantified via their power spectral density and compared with measurements using a commercial accelerometer. We find that a considerable contribution to the CPW resonator noise originates from the mechanical vibrations of the helium surface generated by the pulse tube (PT) cryocooler on the cryostat on which the experiments were performed.
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Submitted 13 July, 2022; v1 submitted 3 November, 2021;
originally announced November 2021.
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Vantablack Shielding of Superconducting Qubit Systems
Authors:
J. M. Kitzman,
J. R. Lane,
T. Stefanski,
N. R. Beysengulov,
D. Tan,
K. W. Murch,
J. Pollanen
Abstract:
Circuit quantum electrodynamics (cQED) experiments on superconducting qubit systems typically employ radiation shields coated in photon absorbing materials to achieve high qubit coherence and low microwave resonator losses. In this work, we present preliminary results on the performance of Vantablack as a novel infrared (IR) shielding material for cQED systems. We compare the coherence properties…
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Circuit quantum electrodynamics (cQED) experiments on superconducting qubit systems typically employ radiation shields coated in photon absorbing materials to achieve high qubit coherence and low microwave resonator losses. In this work, we present preliminary results on the performance of Vantablack as a novel infrared (IR) shielding material for cQED systems. We compare the coherence properties and residual excited state population (or effective qubit temperature) of a single-junction transmon qubit housed in a shield coated with a standard epoxy-based IR absorbing material, i.e. Berkeley Black, to the coherence and effective temperature of the same qubit in a shield coated in Vantablack. Based on a statistical analysis of multiple qubit coherence measurements we find that the performance of the radiation shield coated with Vantablack is comparable in performance to the standard coating. However, we find that in the Vantablack coated shield the qubit has a higher effective temperature. These results indicate that improvements are likely required to optimize the performance of Vantablack as an IR shielding material for superconducting qubit experiments and we discuss possible routes for such improvements. Finally we describe possible future experiments to more precisely quantify the performance of Vantablack to improve the coherences of more complex cQED systems.
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Submitted 13 July, 2022; v1 submitted 18 October, 2021;
originally announced October 2021.
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Noise performance & thermalization of single electron transistors using quantum fluids
Authors:
N. R. Beysengulov,
J. R. Lane,
J. M. Kitzman,
K. Nasyedkin,
D. G. Rees,
J. Pollanen
Abstract:
We report on low-temperature noise measurements of a single electron transistor (SET) immersed in superfluid $^4$He. The device acts as a charge sensitive electrometer able to detect the fluctuations of charged defects in close proximity to the SET. In particular, we measure telegraph switching of the electric current through the device originating from a strongly coupled individual two-level fluc…
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We report on low-temperature noise measurements of a single electron transistor (SET) immersed in superfluid $^4$He. The device acts as a charge sensitive electrometer able to detect the fluctuations of charged defects in close proximity to the SET. In particular, we measure telegraph switching of the electric current through the device originating from a strongly coupled individual two-level fluctuator. By embedding the device in a superfluid helium immersion cell we are able to systematically control the thermalizing environment surrounding the SET and investigate the effect of the superfluid on the SET noise performance. We find that the presence of superfluid $^4$He can strongly suppress the switching rate of the defect by cooling the surrounding phonon bath.
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Submitted 28 September, 2021; v1 submitted 13 October, 2020;
originally announced October 2020.