arXiv subjects

Shifan Qi

Publications and source records attributed to Shifan Qi.

3 recordsLinked to original sources

arXiv2021

Fast and stable charging via a shortcut to adiabaticity

Quantum battery is an emerging subject in the field of quantum thermodynamics, which is applied to charge, store and dispatch energy in quantum systems. In this work, we propose a fast and stable charging protocol based on the adiabatic evolution for the dark state of a three-level quantum battery. It combines the conventional stimulated Raman adiabatic passage (STIRAP) and the quantum transitionless driving technique. The charging process can be accelerated up to nearly one order in magnitude even under constraint of the strength of counter-diabatic driving. To perform the charging protocol in the Rydberg atomic system as a typical platform for STIRAP, the prerequisite driving pulses are modified to avoid the constraint of the forbidden transition. Moreover, our protocol is found to be more robust against the environmental dissipation and dephasing than the conventional STIRAP.

quant-ph↗

arXiv2021

A multifunctional quantum thermal device: with and without inner coupling

A three-level system attached to three thermal baths is manipulated to be a microscopic thermal device integrating a valve, a refrigerator, an amplifier, and a thermometer in the quantum regime, via tuning the inner coupling strength of the system and the temperatures of the external baths. We discuss the role of the inner coupling as well as the steady-state quantum coherence in these thermal functions using the Redfield master equation under a partial secular approximation. A high-sensitive thermometer for the low-temperature terminal can be established without the assistance from the inner coupling of the system. Our study of this multifunctional thermal device provides a deeper insight to the underlying quantum thermodynamics associated with the quantum coherence.

quant-ph↗

arXiv2019

Berry-phase-based quantum gates assisted by transitionless quantum driving

We propose a novel proposal for geometric quantum gates using three- or two-level systems, in which a controllable variable, the detuning between the driving frequency and the atomic energy spacing, is introduced to realize geometric transformations. In particular, we can have two instantaneous eigenstates with opposite eigenvalues constituting a closed loop in the parameter space. The accumulated dynamical phase is then exactly cancelled when the loop is completed, which is beyond the traditional parallel-transport restriction. We apply the transitionless quantum driving, which renders revisions in both amplitudes and phases of the driving fields, to enhance the speed and the fidelity of geometric transformation in both universal single-qubit gates and nontrivial double-qubit gates. Gate fidelity under decoherence is also estimated.

quant-ph↗