Scalable Qumode-Qubit State Transfer and Fast-forward Quantum Fourier Transform using Oscillators

TL;DR

This paper introduces a scalable method for transferring quantum information between multiple qubits and qumodes, enabling faster quantum Fourier transforms and advancing mixed quantum signal processing.

Contribution

It demonstrates improved runtime for qubit-to-qumode state transfer and approximate quantum Fourier transform using multiple qumodes, enhancing scalability and efficiency.

Findings

Transfer to m qumodes reduces runtime to O(2^{n/m})

Approximate quantum Fourier transform scales as O(m2^{n/m}/ε + m^2)

Scalable conversion between discrete and continuous quantum information

Abstract

Transferring the information stored in the expansion coefficients of a multi-qubit state to the coefficients of a continuous-variable state is an important protocol for communicating quantum information. It was shown in previous work how to transfer an $n$-qubit state to a single qumode in $\mathcal{O}(2^n)$ time. We show that by transferring this state to $m$ qumodes, the runtime can be improved to $\mathcal{O}(2^{n/m})$. Furthermore, we demonstrate how multi-qumode state transfer can be used as a subroutine for approximately realizing the $n$-qubits quantum Fourier transform on $m$-qumode with runtime scaling $\mathcal{O}(m2^{n/m}/\epsilon+m^2)$, accelerating qubit quantum Fourier transform using qumodes. This work presents a scalable approach to convert discrete and continuous quantum information between an arbitrary number of qubits and qumodes. It represents a crucial step forward in mixed analog-digital quantum signal processing for computing, sensing, and communication.