Supersolids: unveiling an extraordinary quantum phase of matter

Projektinformationen

Supersolids

ID Finanzhilfevereinbarung: 101055319

DOI

10.3030/101055319

EK-Unterschriftsdatum 30 August 2022

Startdatum 1 November 2022

Enddatum 31 Oktober 2027

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 2 065 000,00

EU-Beitrag

€ 2 065 000,00

Koordiniert durch

UNIVERSITA DEGLI STUDI DI FIRENZE
Italy

Periodic Reporting for period 1 - Supersolids (Supersolids: unveiling an extraordinary quantum phase of matter)

Berichtszeitraum: 2022-11-01 bis 2025-04-30

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Supersolids are a paradoxical quantum phase of matter that combines the properties of superfluids and crystals, searched for long time in quantum solids and many other systems. Recently, we discovered a novel cluster phase in a quantum gas of magnetic atoms which realizes a supersolid. However, the limited size, the inhomogeneity, and the lack of appropriate detection methods have allowed so far to assess only very basic properties of supersolids.
Here I propose an innovative density-phase microscope and original ideas that combine the best of matter-wave and condensed-matter methods to unveil the extraordinary properties of supersolids. With a two-layer superfluid-supersolid configuration we will measure both density and phase of the supersolid. With controllable optical potentials we will realize large, homogeneous crystal geometries in 1D and 2D. With high-resolution optical addressing we will manipulate locally the wavefunction, e. g. creating phase patterns or force fields, and we will follow the local dynamics.
Our main goal is to explore fundamental properties that are largely unknown even theoretically: variable superfluid density under rotation; variable angular momentum of quantized vortices; dissipation-less deformation of the crystal; Josephson effect without barriers; quantum entanglement properties.
We will also attempt the realization of new types of supersolid, to prove the generality of the phenomena: with coupled supersolid layers, we will move towards supersolidity in 3D; using a quasi-2D environment, we will attempt to realize two proposed types of strongly interacting and strongly correlated supersolids.
Our work will establish connections between supersolids and other patterned quantum phases, such as pair-density waves in superconductors and in helium superfluids, intertwined phases in low-dimensional superfluids, and pasta phases in neutron stars. Our work might also open directions for the realization of materials with novel functionalities.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

During the first reporting period we have progressed towards four of the five planned objectives:
Objective 1: Large, homogeneous supersolids from 1D towards 3D - We designed and partially realized a new experimental setup based on novel techniques, which will be soon able to produce larger dipolar supersolids, in a faster and more reliable manner and with the possibility of adding a high-resolution microscope and various types of optical lattices. In the new setup we have achieved laser cooling of dysprosium atoms, and we are proceeding towards Bose-Einstein condensation and supersolidity.
Objective 2: Supersolid microscope - On the original experimental setup, we designed and implemented a novel imaging system with a resolution of about 1.5 microns, which is sufficiently large to resolve the individual sites of the supersolids.
Objective 3: An extraordinary superfluid - We implemented a repulsive optical potential for the dipolar supersolid and shaped it through a DMD-based optical system. The main goal is to realize an annular supersolid to study the peculiar phase-density profiles of a rotating supersolid. First characterizations of a dipolar Bose-Einstein condensate in an annular optical potential are in progress.
Objective 4: An extraordinary crystal - We discovered that a supersolid can sustain coherent Josephson oscillations, similarly to an array of Josephson junctions, and that the superfluid dynamics of the junctions allows to determine directly the so-called superfluid fraction, i.e. the key quantity that distinguishes a supersolid from ordinary superfluids and crystals. We developed a method to excite locally the Josephson junction by phase imprinting on our inhomogeneous (trapped) supersolids, and we surprisingly found that the subsequent Josephson dynamics is the same that would appear in a fully homogeneous systems, simply due to the parity of both trap potential and phase excitation. The peculiar behaviour of the superfluid fraction as a function of the depth of the lattice modulation confirmed that supersolids are indeed a quantum phase of matter distinct from ordinary crystals and superfluids.
The experimental work was complemented by theoretical studies of rotating supersolids and of the roton instability leading to the quantum phase transition from superfluids to supersolids.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

The most significant achievement of the project, so far, is the discovery of the Josephson effect in supersolids and the subsequent measurement of the superfluid fraction, as described in the publication:
Measurement of the superfluid fraction of a supersolid by Josephson effect, G. Biagioni, N. Antolini, B. Donelli, L. Pezzè, A. Smerzi, M. Fattori, A. Fioretti, C. Gabbanini, M. Inguscio, L. Tanzi, G. Modugno, Nature, 629, 773–777 (2024).
We consider the discovery of the Josephson effect in supersolids and the subsequent measurement of the superfluid fraction a breakthrough, for various reasons. 1) The supersolid is the only spontaneous crystal in nature that exhibits the Josephson effect, a proof of its superfluid character. 2) The Josephson effect allowed to measure for the first time the superfluid fraction of a supersolid. 3) Since the Josephson-array structure of supersolids is spontaneous, it possesses a Goldstone mode that opens the way to a new class of Josephson junctions with novel entanglement properties.