Simulating the Interplay of Particle Conservation and Long-Range Coherence

Emanuele G. Dalla Torre and Matthew J. Reagor

Phys. Rev. Lett. 130, 060403 – Published 10 February 2023

Abstract

Lasers and Bose-Einstein condensates (BECs) exhibit macroscopic quantum coherence in seemingly unrelated ways. Lasers possess a well-defined global phase while the number of photons fluctuates. In BECs of atoms, instead, the number of particles is conserved and the global phase is undefined. Here, we use gate-based quantum circuits to create a unified framework that connects lasers and BEC states. Our approach relies on a scalable circuit that measures the total number of particles without destroying long-range coherence. We introduce two complementary probes of global and relative phase coherence, study how they are affected by measurements of the particle number, and implement them on a superconducting quantum computer by Rigetti. We find that particle conservation enhances long-range phase coherence, highlighting a mechanism used by superfluids and superconductors to gain phase stiffness.

Received 23 June 2022
Revised 13 December 2022
Accepted 4 January 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.060403

Physics Subject Headings (PhySH)

Bose-Einstein condensates Quantum coherence & coherence measures Quantum simulation Quantum states of light

Superconducting qubits

Continuous symmetries in condensed matter

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Emanuele G. Dalla Torre ^1,2 and Matthew J. Reagor^3,2

¹Department of Physics and Center for Quantum Entanglement Science and Technology, Bar-Ilan University, 52900 Ramat Gan, Israel
²Superconducting Quantum Materials and Systems Center (SQMS), Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
³Rigetti Computing, 775 Heinz Avenue, Berkeley, California 94710, USA