Environment-Protected Solid State Based Distributed Charge Qubit

TL;DR

This paper introduces a solid state charge qubit system with enhanced coherence and lifetime, utilizing superradiant states to protect against decay and noise, and enabling coherent control through engineered couplings.

Contribution

It presents a novel design of a charge qubit with superradiant states that improve stability and coherence, incorporating environmental effects and non-Hermitian Hamiltonian analysis.

Findings

Superradiant states form at strong continuum coupling, protecting internal states.

The qubit's lifetime and coherence are significantly increased by superradiance.

Environmental noise effects are mitigated through the formation of these states.

Abstract

A novel solid state based charge qubit is presented. The system consists of a one-dimensional wire with a pair of qubits embedded at its center. It is shown that the system supports collective states localized in the left and right sides of the wire and therefore, as a whole, performs as a single qubit. The couplings between the ground and excited states of the two central qubits are inversely proportional making them fully asynchronized and allowing for coherent manipulation and gate operations. Initialization and measurement devices, such as leads and charge detectors, connected to the edges of the wire are modeled by a continuum of energy states. The coupling to the continuum is discussed using the effective non-Hermitian Hamiltonian. At weak continuum coupling, all internal states uniformly acquire small decay widths. This changes dramatically as the coupling strength increases: the width distribution undergoes a sharp restructuring and is no longer uniformly divided among the eigenstates. Two broad resonances localized at the ends of the wire are formed. These superradiant states (analogous to Dicke states in quantum optics), effectively protect the remaining internal states from decaying into the continuum and hence increase the lifetime of the qubit. Environmental noise is introduced by considering random Gaussian fluctuations of electronic energies. The interplay between decoherence and superradiance is studied by solving the stochastic Liouville equation. In addition to increasing the lifetime, the emergence of the superradiant states increases the qubit coherence.