Ancilla-Error-Transparent Controlled Beam Splitter Gate

TL;DR

This paper proposes a new hybrid circuit QED gate using Kerr-cat qubits to realize a controlled beam splitter with high fidelity, enhancing quantum computation and measurement capabilities.

Contribution

It introduces a novel implementation of a controlled beam splitter gate using Kerr-cat qubits, improving error resilience and feasibility in circuit QED systems.

Findings

Proposes a Kerr-cat-based controlled beam splitter gate.

Achieves high fidelity gates comparable to existing operations.

Gate is non-destructive and error-transparent due to phase flip dominance.

Abstract

In hybrid circuit QED architectures containing both ancilla qubits and bosonic modes, a controlled beam splitter gate is a powerful resource. It can be used to create (up to a controlled-parity operation) an ancilla-controlled SWAP gate acting on two bosonic modes. This is the essential element required to execute the `swap test' for purity, prepare quantum non-Gaussian entanglement and directly measure nonlinear functionals of quantum states. It also constitutes an important gate for hybrid discrete/continuous-variable quantum computation. We propose a new realization of a hybrid cSWAP utilizing `Kerr-cat' qubits -- anharmonic oscillators subject to strong two-photon driving. The Kerr-cat is used to generate a controlled-phase beam splitter (cPBS) operation. When combined with an ordinary beam splitter one obtains a controlled beam-splitter (cBS) and from this a cSWAP. The strongly biased error channel for the Kerr-cat has phase flips which dominate over bit flips. This yields important benefits for the cSWAP gate which becomes non-destructive and transparent to the dominate error. Our proposal is straightforward to implement and, based on currently existing experimental parameters, should achieve controlled beam-splitter gates with high fidelities comparable to current ordinary beam-splitter operations available in circuit QED.