[Paper Review] Observation of the Sign Reversal of the Magnetic Correlation in a Driven-Dissipative Fermi Gas in Double Wells

Kantaro Honda, Shintaro Taie+4 more|arXiv (Cornell University)|May 26, 2022

Cold Atom Physics and Bose-Einstein Condensates4 citations

TL;DR

This study demonstrates the sign reversal of magnetic correlations from antiferromagnetic to ferromagnetic in a driven-dissipative ultracold Fermi gas within double-well optical lattices, using controlled on-site two-body losses via photoassociation. The observed ferromagnetic spin correlations are consistent with the long-time formation of a Dicke-type many-body state, showcasing dissipation as a tool for engineering quantum magnetism in open quantum systems.

ABSTRACT

We report the observation of the sign reversal of the magnetic correlation from antiferromagnetic to ferromagnetic in a dissipative Fermi gas in double wells, utilizing the dissipation caused by on-site two-body losses in a controlled manner. We systematically measure dynamics of the nearest-neighbor spin correlation in an isolated double-well optical lattice, as well as a crossover from an isolated double-well lattice to a one-dimensional uniform lattice. In a wide range of lattice configurations over an isolated double-well lattice, we observe a ferromagnetic spin correlation, which is consistent with a Dicke type of correlation expected in the long-time limit. This work demonstrates the control of quantum magnetism in open quantum systems with dissipation.

Motivation & Objective

• To investigate the role of engineered dissipation in driving sign reversal of magnetic correlations in a Fermi gas.
• To experimentally realize and control a driven-dissipative Fermi-Hubbard system with on-site two-body losses.
• To probe the emergence of Dicke-type correlations in open quantum systems through spin correlation measurements.
• To systematically study the crossover from isolated double wells to a 1D uniform lattice under controlled dissipation.
• To provide direct experimental evidence of ferromagnetic spin correlations in dissipative systems, previously inferred only indirectly.

Proposed method

• The experiment uses a six-component degenerate Fermi gas of 173Yb loaded into a tunable optical superlattice to realize dimerized and 1D uniform lattices.
• On-site two-body losses are induced via a photoassociation (PA) laser, which selectively removes singlet-state pairs, thereby modifying spin correlations.
• The dynamics of nearest-neighbor spin correlations are measured using spin-echo techniques with time-of-flight (STO) imaging to extract correlation amplitudes.
• The system is modeled by a dissipative Fermi-Hubbard Hamiltonian with a Lindblad master equation describing two-body loss via the operator $ \hat{L}_{j\sigma\sigma'} = \sqrt{2\gamma} \hat{c}_{j\sigma} \hat{c}_{j\sigma'} $.
• The loss rate $ \gamma $ is controlled by tuning the PA laser intensity and duration, enabling systematic variation of dissipation strength.
• The crossover from isolated double wells to a 1D lattice is achieved by adjusting the long-wavelength lattice depth, allowing control over inter-dimer tunneling.

Experimental results

Research questions

• RQ1 Can engineered dissipation induce a sign reversal of magnetic correlations from antiferromagnetic to ferromagnetic in a Fermi gas?
• RQ2 To what extent does the presence of on-site two-body losses lead to the formation of Dicke-type entangled states in a lattice?
• RQ3 How does the emergence of ferromagnetic spin correlations depend on lattice geometry and dissipation strength?
• RQ4 Is the ferromagnetic spin correlation observable in a 1D uniform lattice under controlled dissipation?
• RQ5 Can the dynamics of spin correlations be used to infer the formation of long-lived Dicke states in open quantum systems?

Key findings

• In isolated double-well lattices, the normalized STO amplitude $ A $ reaches $ -0.042(5) $, indicating a clear sign reversal from antiferromagnetic to ferromagnetic spin correlation.
• The observed ferromagnetic correlation is consistent with the long-time limit of a Dicke-type state, as predicted by theoretical models.
• In the 1D uniform lattice with $ s_{\text{long}}^{(z)} = 0 $, the STO amplitude is $ A = -0.010(6) $, which is negative and statistically significant, confirming ferromagnetic order.
• For a 1D uniform lattice with deeper long-wavelength lattice, $ A = -0.023(5) $, further confirming the persistence of ferromagnetic correlations.
• The suppression of ferromagnetic correlation at low long-lattice depths is attributed to inter-dimer tunneling during PA irradiation, which competes with loss-induced correlation formation.
• The measured dependence of spin correlation on the inter-dimer hopping rate $ 2t_{\text{PA}}t/\hbar $ shows qualitative agreement with theoretical expectations, indicating control over the competition between tunneling and dissipation.