Hamiltonian engineering for robust quantum state transfer and qubit readout in cavity QED

TL;DR

This paper introduces Hamiltonian engineering protocols in cavity QED that enable high-fidelity quantum state transfer and rapid qubit readout, even under environmental noise and weak coupling conditions.

Contribution

It presents new protocols for robust quantum state transfer and qubit readout in cavity QED through Hamiltonian engineering, effective despite strong dephasing and weak coupling.

Findings

High-fidelity state transfer between cavity and qubit achieved.

Decoupling sequences isolate collective modes in large ensembles.

High single-shot fidelity in qubit readout demonstrated.

Abstract

Quantum state transfer into a memory, state shuttling over long distances via a quantum bus, and high-fidelity readout are important tasks for quantum technology. Realizing these tasks is challenging in the presence of realistic couplings to an environment. Here, we introduce and assess protocols that can be used in cavity QED to perform high-fidelity quantum state transfer and fast quantum nondemolition qubit readout through Hamiltonian engineering. We show that high-fidelity state transfer between a cavity and a single qubit can be performed, even in the limit of strong dephasing due to inhomogeneous broadening. We generalize this result to state transfer between a cavity and a logical qubit encoded in a collective mode of a large ensemble of $N$ physical qubits. Under a decoupling sequence, we show that inhomogeneity in the ensemble couples two collective bright states to only two other collective modes, leaving the remaining $N-3$ single-excitation states dark. Moreover, we show that large signal-to-noise and high single-shot fidelity can be achieved in a cavity-based qubit readout, even in the weak-coupling limit. These ideas may be important for novel systems coupling single spins to a microwave cavity.