Observation of a dipolar quantum gas with metastable supersolid properties (1811.02613v2)

Abstract: The competition of dipole-dipole and contact interactions leads to exciting new physics in dipolar gases, well-illustrated by the recent observation of quantum droplets and rotons in dipolar condensates. We show that the combination of the roton instability and quantum stabilization leads under proper conditions to a novel regime that presents supersolid properties, due to the coexistence of stripe modulation and phase coherence. In a combined experimental and theoretical analysis, we determine the parameter regime for the formation of coherent stripes, whose lifetime of a few tens of milliseconds is limited by the eventual destruction of the stripe pattern due to three-body losses. Our results open intriguing prospects for the development of long-lived dipolar supersolids.

• The paper demonstrates metastable supersolid properties in a dipolar dysprosium BEC via tuned roton instability and quantum stabilization.
• It details precise experimental control using Feshbach resonances and magnetic fields to adjust scattering lengths in the BEC.
• Numerical simulations based on the generalized Gross-Pitaevskii equation reproduce coherent stripe formation and the phase’s decay dynamics.

Observation of a Dipolar Quantum Gas with Metastable Supersolid Properties

The paper conducted by L. Tanzi et al. explores the emergence of supersolid properties in dipolar quantum gases. This paper presents a combined experimental and theoretical analysis of a Bose-Einstein Condensate (BEC) formed by Dysprosium atoms, exhibiting metastable supersolid characteristics. The research is grounded in the interplay between dipole-dipole interactions and contact interactions, which lead to novel phases that challenge conventional understanding in condensed matter physics.

Key Research Outcomes

1. Supersolid Phase Observation: The paper reports the observation of a dipolar BEC that transitions into a metastable phase with supersolid properties under certain conditions. This transition is facilitated by the roton instability, balanced by quantum stabilization mechanisms.
2. Experimental Regime and Setup: The experiments used a highly dipolar element, $^{162}$Dy, in a trapped BEC with adjustable interactions via a Feshbach resonance. Precise control over the scattering length through magnetic fields allowed the exploration of different interaction regimes. The developed methodology involved transitioning the BEC through instability regions to achieve the supersolid phase.
3. Coherent Stripe Formation: The authors observed coherent stripe patterns in the density distribution of the quantum gas, indicative of the simultaneous presence of superfluidity and crystalline order—a haLLMark of supersolid phases. These patterns evolved in a limited range of interaction strengths and showcased finite lifetimes due to three-body losses.
4. Numerical Simulations: Complementing experimental observations, numerical simulations using the generalized Gross-Pitaevskii equation incorporating dipolar and quantum fluctuation effects reproduced the key experimental features. The simulations provided insights into the conditions fostering coherent stripe formation and their subsequent decay due to losses.

Implications and Future Directions

• Novel Quantum Phases: The results extend the understanding of possible quantum phases in strongly interacting systems, supporting the theory that supersolid properties can emerge from intrinsic interactions without external modulation.
• Experimental Verification: This work contributes to the broader effort in verifying supersolid phases experimentally. It contrasts with previous attempts where supersolidity was induced through extrinsic mechanisms such as optical lattices or cavities.
• Potential Applications: Understanding and controlling supersolid properties in dipolar gases could have implications for quantum simulation of complex materials and exotic phases of matter.
• Path Forward: Future investigations could focus on achieving longer lifetimes for the supersolid phase, perhaps by exploring isotopes with lower inelastic collision rates or adjusting trapping configurations. Moreover, accurately testing for superfluidity within the stripe patterns remains a critical objective to fully validate the supersolid nature.

In conclusion, the observation of a metastable supersolid phase in a dipolar BEC representation is remarkable progress towards understanding complex quantum phases. This research provides a foundation for future experiments aimed at exploring the properties and potential applications of dipolar supersolids.