Single-photon pulse induced giant response in N$>$100 qubit system

TL;DR

This paper models how a single photon can induce a giant response in a large qubit system near a quantum phase transition, enabling single-shot quantum detection through amplified magnetic noise.

Contribution

It introduces a time-dependent model predicting giant susceptibility and single-shot detection in large qubit systems engineered near a quantum phase transition.

Findings

Single photon absorption can trigger a macroscopic change in the qubit system.

Giant susceptibility occurs near the quantum phase transition point.

Amplified magnetic noise enables single-shot quantum measurement.

Abstract

The temporal dynamics of large quantum systems perturbed weakly by a single excitation can give rise to unique phenomena at the quantum phase boundaries. Here, we develop a time-dependent model to study the temporal dynamics of a single photon interacting with a defect within a large system of interacting spin qubits (N$>$100). Our model predicts a new quantum resource, giant susceptibility, when the system of qubits is engineered to simulate a first-order quantum phase transition (QPT). We show that the absorption of a single photon pulse by an engineered defect in the large qubit system can nucleate a single shot quantum measurement through spin noise read-out. This concept of a single-shot detection event ("click") is different from parameter estimation which requires repeated measurements. The crucial step of amplifying the weak quantum signal occurs by coupling the defect to a system of interacting qubits biased close to a QPT point. The macroscopic change in long-range order during the QPT generates amplified magnetic noise, which can be read out by a classical device. Our work paves the way for studying the temporal dynamics of large quantum systems interacting with a single-photon pulse.