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arXiv:2611.02163

Sound-wave interference reveals the symmetry of a quantum transition

Sergei Studenikin, Yousef Karimi Yonjali, Alex Bogan, Andy Sachrajda, Shabir Barzanjeh

quant-phcond-mat.mes-hallSubmitted Nov 1, 2026• Announced Nov 3, 2026
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Abstract

A single sound quantum emitted from two places interferes with itself, like a particle passing through two slits. The fringe position reveals whether the sources emit with the same sign (symmetric) or opposite signs (antisymmetric). Knowing this symmetry is important because qubits in solids lose energy by emitting such sound quanta, phonons. For a qubit shared between two sites, antisymmetric emission cancels at long wavelengths, suppressing energy loss, whereas symmetric emission does not. Lifetime measurements give only the total loss and cannot distinguish them. Such fringes appear in double quantum dots, but their position has not been analysed. Here we measure it for single phonons emitted as one hole tunnels between two gallium arsenide quantum dots. Using a quantitative model of sound focusing in the crystal, we find that the two dots emit antisymmetrically, as expected for a moving charge, with only a small symmetric part. Spin-flip transitions in a magnetic field weaken the fringes without shifting them. For double-dot charge qubits, antisymmetric emission is predicted to reduce phonon losses strongly at the frequencies where qubits operate, and phonon interferometry gives a direct way to measure how qubits release energy and to design longer-lived qubits.

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A single sound quantum emitted from two places interferes with itself, like a particle passing through two slits. The fringe position reveals whether the sources emit with the same sign (symmetric) or opposite signs (antisymmetric). Knowing this symmetry is important because qubits in solids lose energy by emitting such sound quanta, phonons. For a qubit shared between two sites, antisymmetric emission cancels at long wavelengths, suppressing energy loss, whereas symmetric emission does not. Lifetime measurements give only the total loss and cannot distinguish them. Such fringes appear in double quantum dots, but their position has not been analysed. Here we measure it for single phonons emitted as one hole tunnels between two gallium arsenide quantum dots. Using a quantitative model of sound focusing in the crystal, we find that the two dots emit antisymmetrically, as expected for a moving charge, with only a small symmetric part. Spin-flip transitions in a magnetic field weaken the fringes without shifting them. For double-dot charge qubits, antisymmetric emission is predicted to reduce phonon losses strongly at the frequencies where qubits operate, and phonon interferometry gives a direct way to measure how qubits release energy and to design longer-lived qubits.
Hole-phonon interactions play an important role in transport and decoherence processes in semiconductor quantum dots. Here we investigate hole-phonon coupling in a gate-defined GaAs double quantum dot integrated with a quantum point contact charge sensor. Under finite source-drain bias, pronounced oscillatory stripe patterns appear near specific charge transition regions in the charge stability diagram. We attribute these oscillations to phonon emission during inelastic interdot tunneling. A theoretical model including piezoelectric hole-phonon coupling reproduces the observed patterns. Furthermore, our analysis shows that the oscillations emerge only in particular charge configurations. Our results provide direct insight into phonon-assisted transport and coherent hole-phonon interactions in semiconductor quantum dots.
Many quantum dot qubits operate in regimes where the energy splittings between qubit states are large and phonons can be the dominant source of decoherence. The recently proposed charge quadrupole qubit, based on one electron in a triple quantum dot, employs a highly symmetric charge distribution to suppress the influence of long-wavelength charge noise. To study the effects of phonons on the charge quadrupole qubit, we consider Larmor and Ramsey pulse sequences to identify favorable operating parameters. We show that phonon-induced decoherence increases with the qubit frequency, in contrast to the effects of charge noise. We also show that there is an optimum value of the tunnel coupling of the qubit at which the decohering effects of phonons and charge noise are small enough to be consistent with single qubit gate fidelities > 99.99%.
Long-distance transfer of quantum information in architectures based on quantum dot spin qubits will be necessary for their scalability. One way of achieving this goal is to simply move the electron between two quantum registers. Precise control over the process of shuttling such a single electron through a chain of tunnel-coupled quantum dots is possible when interdot energy detunings are changed adiabatically. The deterministic character of shuttling is, however, endangered by the open nature of the system, as the transferred electron is coupled to thermal reservoirs: sources of fluctuations of electric fields and lattice vibrations. We present a comprehensive analysis showing how the electron transfer between two voltage-controlled quantum dots is affected by electron-phonon scattering and interaction with sources of 1/f1/f1/f and Johnson charge noise in both detuning and tunnel coupling. The electron-phonon scattering turns out to be irrelevant in Si quantum dots, with charge noise dominating the dynamics of the system at slow detuning sweep, when the electron spends more time delocalized between the dots (i.e., near the anticrossing of the tunnel-coupled states). Competition between the effects of charge noise and the Landau-Zener effect leads to an existence of an optimal detuning sweep rate, leading to minimal probability of leaving the electron behind. In GaAs quantum dots, on the other hand, piezoelectric coupling to phonons is strong enough to make the processes of interdot transfer assisted by phonon emission and absorption dominate over transitions caused by charge noise. The probability of leaving the electron behind then depends monotonically on detuning the sweep rate over a broad range of rates, and values much smaller than in silicon can be obtained for slow sweeps. However, after taking into account limitations on transfer time imposed by the need for preservation of a shuttled electron's spin coherence, the minimal probabilities of leaving the electron behind in both GaAs- and Si-based double quantum dots turn out to be of the same order of magnitude. Bringing them down below ${10}^{\ensuremath{-}3}$ requires temperatures $\ensuremath{\le}100$ mK and tunnel couplings above $20\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{eV}$.
We report on an optimal single-electron charge qubit for a solid-state double quantum dot (DQD) system and analyse its dynamics under a time-dependent linear detuning, using GPU accelerated numerical solutions to the time-dependent Schrödinger equation. The optimal qubit is found to have basis states defined as the symmetric and antisymmetric linear combinations of the lowest energy bonding and anti-bonding states of the DQD at zero bias. In contrast to charge qubits defined by the two localised ground states of the uncoupled DQD, this choice of the basis causes the resulting dynamics to have a maximal overlap with an idealised two-state model. Our optimal qubit basis states are not localised to a single quantum dot and, as such, initialising the qubit requires a particular sequence of gate pulses to take the system from an initial fiducial state of the DQD to the logical 000 or 111. We determine this sequence using pulses that incorporate the expected experimental finite rise times. We also show how to perform arbitrary single qubit operations on the Bloch sphere using spin-echo type pulsing, allowing us to obtain any qubit state with at most two single pulses. Measurement of the optimal qubits is achieved by determining the probability of finding the electron in one of the dots.
A double quantum dot device is a tunable two-level system for electronic energy states. A dc electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.