Multi-output microwave single-photon source using superconducting circuits with longitudinal and transverse couplings

TL;DR

This paper proposes a multi-output microwave single-photon source using superconducting circuits with unique longitudinal and transverse couplings, enabling efficient photon blockade and entanglement for quantum information applications.

Contribution

It introduces a novel superconducting circuit design with quadratic coupling and strong nonlinearity, producing pure single-photon states and entanglement, differing from traditional models.

Findings

Effective quadratic coupling enhances photon blockade.

Output fields show strong sub-Poissonian statistics and antibunching.

First-excited state is a pure single-photon Fock state.

Abstract

Single-photon devices at microwave frequencies are important for applications in quantum information processing and communication in the microwave regime. In this work, we describe a proposal of a multi-output single-photon device. We consider two superconducting resonators coupled to a gap-tunable qubit via both its longitudinal and transverse degrees of freedom. Thus, this qubit-resonator coupling differs from the coupling in standard circuit quantum-electrodynamic systems described by the Jaynes-Cummings model. We demonstrate that an effective quadratic coupling between one of the normal modes and the qubit can be induced, and this induced second-order nonlinearity is much larger than that for conventional Kerr-type systems exhibiting photon blockade. Assuming that a coupled normal mode is resonantly driven, we observe that the output fields from the resonators exhibit strong sub-Poissonian photon-number statistics and photon antibunching. Contrary to previous studies on resonant photon blockade, the first-excited state of our device is a pure single-photon Fock state rather than a polariton state, i.e., a highly hybridized qubit-photon state. In addition, it is found that the optical state truncation caused by the strong qubit-induced nonlinearity can lead to an entanglement between the two resonators, even in their steady state under the Markov approximation.