S. N. Coppersmith

University of Wisconsin–Madison

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Mark Friesen

University of Wisconsin–Madison

225

M. A. Eriksson

University of Wisconsin–Madison

159

D. E. Savage

University of Wisconsin–Madison

115

M. G. Lagally

University of Wisconsin–Madison

Robert Joynt

University of Wisconsin–Madison

Daniel R. Ward

HRL Laboratories (United States)

John King Gamble

IonQ (United States)

C. B. Simmons

University of Wisconsin–Madison

L. M. K. Vandersypen

QuTech

Brandur Thorgrimsson

UNSW Sydney

Cooperative Institutions

University of Wisconsin–Madison

171

Delft University of Technology

QuTech

UNSW Sydney

University of California, Berkeley

Lawrence Berkeley National Laboratory

Harvard University

University of Chicago

Centre for Quantum Computation and Communication Technology

Intel (United States)

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Nanoelectronic modeling (NEMO) for high fidelity simulation of solid-state quantum computing gates

Gerhard Klimeck Fabiano Oyafuso Paul von Allmen Seungwon Lee Tim Boykin

High fidelity

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Low-temperature phase of a stacked triangular Ising antiferromagnet

Physical review. B, Condensed matter (1985)

S. N. Coppersmith

We have investigated a model consisting of planes of Ising spins with antiferromagnetic nearest-neighbor interactions on a triangular lattice connected by nearest-neighbor ferromagnetic bonds in the third direction. It is shown that Landau theory, mean-field theory, and conventional low-temperature expansions are not reliable for this model. We have also studied a class of one-dimensional frustrated Ising models which have low-temperature expansions with irrational coefficients, indicating that the usual method of counting excitations about ground-state configurations cannot be used to construct their low-temperature series. The results from the one-dimensional models are used to obtain bounds on the free energy and information about the magnetization of the three-dimensional model at low temperatures.

Hexagonal Lattice

Lattice (music)

10.1103/physrevb.32.1584

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Effects of Temperature Fluctuations on Charge Noise in Quantum Dot Qubits

arXiv (Cornell University) (2023)

D. L. Mickelsen Hervé M. Carruzzo S. N. Coppersmith Clare C. Yu

Silicon quantum dot qubits show great promise but suffer from charge noise with a 1/f^\alpha spectrum, where f is frequency and \alpha \lesssim 1. It has recently been proposed that 1/f^\alpha noise spectra can emerge from a few thermally activated two-level fluctuators in the presence of sub-bath temperature fluctuations associated with a two-dimensional electron gas (2DEG)~\cite{Ahn2021}. We investigate this proposal by doing Monte Carlo simulations of a single Ising spin in a bath with a fluctuating temperature. We find that to obtain noise with a $1/f^\alpha$ spectrum with $alpha \lesssim 1 down to low frequencies, the duration of temperature fluctuations must be comparable to the inverse of the lowest frequency at which the noise is measured. This result is consistent with an analytic calculation in which the fluctuator is a two-state system with dynamics governed by time-dependent switching rates. In this case we find that the noise spectrum follows a Lorentzian at frequencies lower than the inverse of the average duration of the lowest switching rate. We then estimate relaxation times of thermal fluctuations by considering thermal diffusion in an electron gas in a confined geometry. We conclude that temperature fluctuations in a 2DEG sub-bath would require an unphysically long duration to be consistent with experimental measurements of 1/f-like charge noise in quantum dots at frequencies extending well below 1 Hz.

Thermal fluctuations

10.48550/arxiv.2305.14515

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Achieving high fidelity single qubit gates in strongly driven silicon quantum dot qubits

Bulletin of the American Physical Society (2018)

Yuan-Chi Yang Mark Friesen S. N. Coppersmith

High fidelity

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Signatures of atomic-scale structure in the energy dispersion and coherence of a Si quantum-dot qubit

Physical review. B./Physical review. B (2018)

J. C. Abadillo-Uriel Brandur Thorgrimsson Dohun Kim L. W. Smith C. B. Simmons

Valley splitting affects the energy dispersion of silicon quantum dot qubits, and occasionally manifests itself through some striking features. Here, the authors observe a strong correlation between unexpected ``sweet spots'' and ``hot spots'' in the coherence rates of a quantum-dot hybrid qubit and in some anomalous features in the energy dispersion. Through tight-binding simulations, they are able to attribute such effects to disorder at the quantum-well interface and speculate on the possibility of harnessing disorder to enhance qubit coherence times.

Coherence time

10.1103/physrevb.98.165438

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Perturbative and variational calculations of charge fluctuations of an extended Hubbard model

Physical review. B, Condensed matter (1990)

S. N. Coppersmith P. B. Littlewood

A charge-transfer instability that occurs in an extended Hubbard model with strong nearest-neighbor repulsions is examined nonperturbatively using variational wave functions. We show that a single mode approximation applied to a Hartree-Fock wave function accurately reproduces previous weak-coupling results on excitonic spectra. We then apply the method to a Gutzwiller variational wave function and extract information about the dynamic charge fluctuations in the intermediate and strong-coupling regimes.

10.1103/physrevb.41.2646

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Lifting of spin blockade by charged impurities in Si-MOS double quantum dot devices

Physical review. B./Physical review. B (2020)

Cameron King Joshua Schoenfield M. J. Calderón Belita Koiller André Saraiva

One obstacle that has slowed the development of electrically gated metal-oxide-semiconductor (MOS) singlet-triplet qubits is the frequent lack of observed spin blockade, even in samples with large singlet-triplet energy splittings. We present theoretical and experimental evidence that this problem in MOS double quantum dots can be caused by stray positive charges in the oxide, inducing accidental localized levels near the device's active region that lead to the lifting of the spin blockade. We also present evidence that these effects can be mitigated by device design modifications, such as overlapping gates.

10.1103/physrevb.101.155411

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Quantum Algorithms Based on Physical Processes

Eric Bach S. N. Coppersmith Mark Friesen Robert Joynt

10.21236/ada608050

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Strategies for Enhancing Spin-Shuttling Fidelities in Si / Si Ge Quantum Wells with Random-Alloy Disorder

PRX Quantum (2024)

Merritt P. Losert Max Oberländer Julian D. Teske M. Volmer Lars R. Schreiber

Coherent coupling between distant qubits is needed for many scalable quantum computing schemes. In quantum dot systems, one proposal for long-distance coupling is to coherently transfer electron spins across a chip in a moving dot potential. Here, we use simulations to study challenges for spin shuttling in Si/SiGe heterostructures caused by the valley degree of freedom. We show that for devices with valley splitting dominated by alloy disorder, one can expect to encounter pockets of low valley splitting, given a long-enough shuttling path. At such locations, intervalley tunneling leads to dephasing of the spin wave function, substantially reducing the shuttling fidelity. We show how to mitigate this problem by modifying the heterostructure composition, or by varying the vertical electric field, the shuttling velocity, the shape and size of the dot, or the shuttling path. We further show that combinations of these strategies can reduce the shuttling infidelity by several orders of magnitude, putting shuttling fidelities sufficient for error correction within reach. Published by the American Physical Society 2024

10.1103/prxquantum.5.040322

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Single-Shot Measurement of Triplet-Singlet Relaxation in aSi/SiGeDouble Quantum Dot

Physical Review Letters (2012)

J. R. Prance Zhan Shi C. B. Simmons D. E. Savage M. G. Lagally

We investigate the lifetime of two-electron spin states in a few-electron Si/SiGe double dot. At the transition between the (1,1) and (0,2) charge occupations, Pauli spin blockade provides a readout mechanism for the spin state. We use the statistics of repeated single-shot measurements to extract the lifetimes of multiple states simultaneously. When the magnetic field is zero, we find that all three triplet states have equal lifetimes, as expected, and this time is ~10 ms. When the field is nonzero, the T(0) lifetime is unchanged, whereas the T- lifetime increases monotonically with the field, reaching 3 sec at 1 T.

Pauli exclusion principle

Zero (linguistics)

10.1103/physrevlett.108.046808

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Citations (86)