High-fidelity bosonic quantum state transfer using imperfect transducers and interference

Hoi-Kwan Lau,Aashish A Clerk

doi:10.1038/s41534-019-0143-1

Abstract

We consider imperfect two-mode bosonic quantum transducers that cannot completely transfer an initial source-system quantum state due to insufficient coupling strength or other Hamiltonian non-idealities. We show that such transducers can generically be made perfect by using interference and phase-sensitive amplification. Our approach is based on the realization that a particular kind of imperfect transducer (one which implements a swapped quantum non-demolition (QND) gate) can be made into a perfect one-way transducer using feed-forward and/or injected squeezing. We show that a generic imperfect transducer can be reduced to this case by repeating the imperfect transduction operation twice, interspersed with amplification. Crucially, our scheme only requires the ability to implement squeezing operations and/or homodyne measurement on one of the two modes involved. It is thus ideally suited to schemes where there is an asymmetry in the ability to control the two coupled systems (e.g., microwave-to-optics quantum state transfer). We also discuss a correction protocol that requires no injected squeezing and/or feed-forward operation.

Highlights

The ability to interface disparate quantum systems would allow one to harness their respective advantages, and could have a transformative effect on quantum science
We start by considering the simplest kind of transducer, where the interaction of two bosonic modes a^1, a^2 is described by a Gaussian unitary transformation; the additional effect of environmental noise will be treated later
We will use throughout the nomenclature of a scattering process; the results are applied to the time-domain case by realizing that input modes correspond to initial time mode operators, i.e., a^in a^ð0Þ and a^out a^ðτÞ 1⁄4 UbyðτÞa^ð0ÞUbðτÞ for some evolution operator Ub corresponding to an evolution time τ

Summary

Introduction

The ability to interface disparate quantum systems would allow one to harness their respective advantages, and could have a transformative effect on quantum science. While local operations always exist to make our transducer quadrature-diagonal, in general these operations will require the injecting a squeezed state into mode 1, such that q^i1n ! This transformation belongs to class [[2, 1]] because each output mode consists of two transmitted and one reflected quadratures.

Results

Conclusion