Sampling and scrambling on a chain of superconducting qubits

TL;DR

This paper investigates a superconducting qubit circuit called the Josephson sampler, which embeds vectors into entangled states, samples from them, and demonstrates its capabilities in generating complex quantum states and chaos on a 16-qubit chip.

Contribution

It introduces the Josephson sampler circuit and evaluates its fidelity, entanglement, and expressiveness in generating Haar random unitaries and quantum chaos on superconducting qubits.

Findings

High fidelity and entanglement achieved on 16-qubit chip

Successfully generates Haar random unitaries and exhibits quantum chaos

Suitable for first-generation superconducting architectures

Abstract

We study a circuit, the Josephson sampler, that embeds a real vector into an entangled state of n qubits, and optionally samples from it. We measure its fidelity and entanglement on the 16-qubit ibmqx5 chip. To assess its expressiveness, we also measure its ability to generate Haar random unitaries and quantum chaos, as measured by Porter-Thomas statistics and out-of-time-order correlation functions. The circuit requires nearest-neighbor CZ gates on a chain and is especially well suited for first-generation superconducting architectures.