Simulating long-range coherence of atoms and photons in quantum computers

TL;DR

This paper introduces a scalable quantum computing framework that simulates long-range quantum coherence in lasers and Bose-Einstein condensates by mapping bosonic particles to qubits, enabling phase coherence measurement without destroying the state.

Contribution

A unified, scalable quantum circuit approach to simulate and measure long-range coherence in bosonic systems like lasers and BECs, using particle-number conserving mappings.

Findings

Particle-number conservation enhances phase coherence.

The framework measures global and relative phase coherence.

Demonstration on a Rigetti quantum computer confirms the approach.

Abstract

Lasers and Bose-Einstein condensates (BECs) exhibit macroscopic quantum coherence in seemingly unrelated ways. Lasers possess a well-defined global phase and are characterized by large fluctuations in the number of photons. In BECs of atoms, instead, the number of particles is conserved and the global phase is undefined. Here, we present a unified framework to simulate lasers and BECs states in gate-based quantum computers, by mapping bosonic particles to qubit excitations. Our approach relies on a scalable circuit that measures the total number of particles without destroying long-range coherence. We introduce complementary probes to measure the global and relative phase coherence of a quantum state, and demonstrate their functionality on a Rigetti quantum computer. Our work shows that particle-number conservation enhances long-range phase coherence, highlighting a mechanism used by superfluids and superconductors to gain phase stiffness.