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arXiv:1906.06271 · npj Quantum Information

Tunable phonon-induced steady-state coherence in a double-quantum-dot charge qubit

Archak Purkayastha, Giacomo Guarnieri, Mark T. Mitchison, Radim Filip, John Goold

Published Mar 13, 2020• 79 citations
arXivHTMLPDF

Abstract

Abstract Charge qubits can be created and manipulated in solid-state double-quantum-dot (DQD) platforms. Typically, these systems are strongly affected by quantum noise stemming from coupling to substrate phonons. This is usually assumed to lead to decoherence towards steady states that are diagonal in the energy eigenbasis. In this article, we show, to the contrary, that due to the presence of phonons the equilibrium steady state of the DQD charge qubit spontaneously exhibits coherence in the energy eigenbasis with high purity. The magnitude and phase of the coherence can be controlled by tuning the Hamiltonian parameters of the qubit. The coherence is also robust to the presence of fermionic leads. In addition, we show that this steady-state coherence can be used to drive an auxiliary cavity mode coupled to the DQD.

DOI
10.1038/s41534-020-0256-6

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Abstract Charge qubits can be created and manipulated in solid-state double-quantum-dot (DQD) platforms. Typically, these systems are strongly affected by quantum noise stemming from coupling to substrate phonons. This is usually assumed to lead to decoherence towards steady states that are diagonal in the energy eigenbasis. In this article, we show, to the contrary, that due to the presence of phonons the equilibrium steady state of the DQD charge qubit spontaneously exhibits coherence in the energy eigenbasis with high purity. The magnitude and phase of the coherence can be controlled by tuning the Hamiltonian parameters of the qubit. The coherence is also robust to the presence of fermionic leads. In addition, we show that this steady-state coherence can be used to drive an auxiliary cavity mode coupled to the DQD.
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High-Fidelity Single-Qubit Gates Via Strongly Driving of a Double Quantum Dot Hybrid Qubit with 1/f1/f1/f Charge Noise
Semiconductor double quantum dot hybrid qubits are promising candidates for high-fidelity quantum computing. However, their performance is limited by charge noise, which is ubiquitous in solid-state devices, and phonon-induced dephasing. Here we explore methods for improving the quantum operations of a hybrid qubit, using strong microwave driving to enable gate operations that are much faster than decoherence processes. Using numerical simulations and a theoretical method based on a cumulant expansion, we analyze qubit dynamics in the presence of 1/f1/f1/f charge noise, which forms the dominant decoherence mechanism in many solid-state devices. We show that, while strong-driving effects and charge noise both reduce the quantum gate fidelity, simple pulse-shaping techniques effectively suppress the strong-driving effects. Moreover, a broad AC sweet spot emerges when the detuning parameter and the tunneling coupling are driven simultaneously. Taking into account phonon-mediated noise, we find that it should be possible to achieve XπX_{\pi}Xπ​ gates with fidelities higher than 99.9%99.9\%99.9%.
We theoretically study the non-equilibrium correlations and entanglement between distant semiconductor qubits in a one-dimensional coupled-mechanical-resonator chain. Each qubit is defined by a double quantum dot (DQD) and embedded in a mechanical resonator. The two qubits can be coupled, correlated and entangled through phonon transfer along the resonator chain. We calculate the non-equilibrium correlations and steady-state entanglement at different phonon-phonon coupling rates, and find a maximal steady entanglement induced by a population inversion. The results suggest that highly tunable correlations and entanglement can be generated by phonon-qubit hybrid system, which will contribute to the development of mesoscopic physics and solid-state quantum computation.
We investigate the decoherence of a charge qubit in a double quantum dot which is formed in a free-standing semiconductor slab. The dots are spatially arranged to align along a particular direction. Confined phonons in the slab have a remarkable influence on the dynamics of a qubit system. We show that the decoherence of such a qubit strongly depends on the positions of the dots. By varying the tunnel coupling, the decoherence differs significantly in laterally and vertically coupled quantum dots. A robust qubit is further achieved due to suppression of electron-phonon coupling. Moreover, the coherent evolution of the system is analyzed by modulating the interdot direction.