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Physical review. B./Physical review. B

Photon-assisted electron transport across a quantum phase transition

Lei‐Lei Nian, Shiqian Hu, Long Xiong, Jing‐Tao Lü, Bo Zheng

Published Aug 28, 2023• 7 citations
Publisher

Abstract

Quantum-dot circuit quantum electrodynamics (QD-cQED) offers an important platform for achieving photon-to-electron conversion in the linear regime, but it has been challenging to efficiently control the photocurrent. Here, we propose a nonlinear QD-cQED setup of a double quantum dot system capacitively coupled to a microwave resonator containing Kerr nonlinearity. By means of the quantum master equation, we derive a general formulation to establish the connection between photon excitation and generated photocurrent. It is revealed that the excitation of photons undergoes a first-order quantum phase transition, which provides a mechanism to adjust the photon-assisted electron transport and leads to an increase in the photocurrent. In contrast to the linear QD-cQED setups, the enhancement in photocurrent benefits from the enhanced energy transfer from photon to electron systems near the phase transition. Our results establish the quantum phase transition as an invaluable tool for optimizing the photon-to-electron conversion in QD-cQED devices.

DOI
10.1103/physrevb.108.085430

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Quantum-dot circuit quantum electrodynamics (QD-cQED) offers an important platform for achieving photon-to-electron conversion in the linear regime, but it has been challenging to efficiently control the photocurrent. Here, we propose a nonlinear QD-cQED setup of a double quantum dot system capacitively coupled to a microwave resonator containing Kerr nonlinearity. By means of the quantum master equation, we derive a general formulation to establish the connection between photon excitation and generated photocurrent. It is revealed that the excitation of photons undergoes a first-order quantum phase transition, which provides a mechanism to adjust the photon-assisted electron transport and leads to an increase in the photocurrent. In contrast to the linear QD-cQED setups, the enhancement in photocurrent benefits from the enhanced energy transfer from photon to electron systems near the phase transition. Our results establish the quantum phase transition as an invaluable tool for optimizing the photon-to-electron conversion in QD-cQED devices.
Coupling of quantum-dot circuits to microwave photons enables us to investigate photon-assisted quantum transport. Here, we revisit this typical circuit quantum electrodynamical setup by introducing the Kerr nonlinearity of photons. By exploiting quantum critical behavior, we propose a powerful scheme to control the power-harvesting efficiency in the microwave regime, where the driven-dissipative optical system acts as an energy pump. It drives electron transport against a load in the quantum-dot circuit. The energy transfer and, consequently, the harvesting efficiency are enhanced near the critical point. As the critical point moves towards to low input power, high efficiency within experimental parameters is achieved. Our results complement fundamental studies of photon-to-electron conversion at the nanoscale and provide practical guidance for designs of integrated photoelectric devices through quantum criticality.
We study cavity quantum electrodynamics (cQED) in coupled quantum dot--microcavity systems under electrical readout. Strict resonant excitation of a target quantum dot (QD) allows us to monitor the photocurrent response of a single emitter in the quantum limit of light-matter interaction. We find a strong anticorrelation between radiative recombination and nonradiative tunnel escape of photoexcited carries which can be controlled by cQED effects in the Purcell regime. In fact, cavity-enhanced radiative emission from a QD results in a weaker photocurrent signal which reflects the cQED controlled competition between radiative and nonradiative recombination at the single emitter level.
Abstract We propose and analyze an effective scheme to enhance Kerr nonlinearity with a single quantum dot (QD) coupled to a gain cavity. Under the weak-excitation approximation, we derive the analytic formulas used to determine the coefficient of the nonlinear transmission by employing the perturbation technique. Using experimentally achievable parameters, we identify the conditions under which a QD gain cavity coupled system allows us to modify the linear transmission of the input probe field and enhance the Kerr nonlinearity beyond what is achievable in a QD loss cavity system. It is found that enhanced optical Kerr nonlinearity with high linear transmission rate and suppressed nonlinear absorption can be achievable even in the case of weak coupling between QD and gain cavity. The present results illustrate the potential to utilize gain cavity for enhancing optical Kerr nonlinearities and controlling the transmission of light, as well as guide the design of optical devices.
We theoretically study the photon-assisted transport (PAT) in a double quantum dot (QD) which is conditionally controlled by the optical excitation in an adjacent QD. Based on a real three-QD model, a double-electron level configuration needed for the conditional PAT is designed. Interesting conditional dynamics are demonstrated for the double QD and its adjacent QD. Depending on various conditional frequencies, the conditional behaviors can be manifested as the current peaks or collapses of the PAT. They correspond to coherent excitations or trapping of double-electron states. Our results present a possible way to optically manipulate electron states and monitor them via the signals of current spectrum.
This thesis investigates hybrid circuit quantum electrodynamics (cQED) as a versatile platform that unites superconducting resonators with semiconductor quantum dots. The central motivation is to harness strong light-matter coupling at the single-photon level, which enables coherent photon-qubit interactions and paves the way for quantum technologies in computation, communication, and sensing. The first part of this work combines hybrid cQED with holes in planar Ge/SiGe, a material system that has only recently become accessible for quantum devices. Planar Ge offers unique advantages for this purpose and has attracted considerable attention in the context of quantum computing. In contrast, its potential for hybrid cQED has remained largely unexplored, making the present work one of the first demonstrations of strong light-matter interaction in this platform. Within this framework, we demonstrate strong charge-photon coupling in planar Ge by observing vacuum Rabi splitting between a hole charge qubit based on a double quantum dot (DQD) and a microwave resonator. We employ a frequency-tunable high-impedance resonator to perform qubit spectroscopy, enabling systematic exploration of coupling regimes and confirming device controllability. In addition, we use this setup to carry out excited-state spectroscopy of strongly correlated states in the DQD, revealing the formation of Wigner molecules and illustrating how the hybrid architecture can be harnessed to access many-body physics. While these experiments in Ge demonstrate how strong coupling can be harnessed to explore qubit physics and correlated states, they also exemplify the wider potential of hybrid cQED. A particularly pressing application is in quantum optics, where efficient single-photon detectors are still lacking in the microwave regime. Such detectors are essential for enabling experiments in quantum communication and microwave quantum optics. In the second part of this thesis, we address this challenge by realizing a photodetector based on a GaAs DQD coupled to a superconducting resonator. The detector operates via photon-to-charge conversion and achieves efficiencies approaching unity. Strong coupling plays a central role by ensuring that incoming photons are absorbed before being lost to the environment, which is key to the high performance of the detector. We further exploit the frequency tunability of the resonator to investigate device performance and identify the parameters that optimize detection efficiency. The broader impact of this work lies in advancing quantum technologies that rely on coherent microwave photons. Applications include spin qubit readout, long-distance photon-mediated coupling, quantum communication, and microwave quantum optics. Looking forward, planar Ge is identified as a highly competitive platform for hybrid cQED. Future directions include the development of single-photon sources, quantum- limited detectors, and analog quantum simulators based on engineered resonator-qubit arrays.
We investigate photon-mediated transport processes in a hybrid circuit-QED structure consisting of two double quantum dots coupled to a common microwave cavity. Under suitable resonance conditions, electron transport in one double quantum dot is facilitated by the transport in the other dot via photon-mediated processes through the cavity. We calculate the average current in the quantum dots, the mean cavity photon occupation, and the current cross-correlations with both a full numerical simulation and a recursive perturbation scheme that allows us to include the influence of the cavity order-by-order in the couplings between the cavity and the quantum dot systems. We can then clearly identify the photon-mediated transport processes.