![]() ![]() These modulations appeared on a timescale of approximately 150 ms. Under this condition, they found that the density modulations that formed looked like droplets-indicative of a supersolid. To study the system, the team used two imaging techniques: Faraday phase-contrast imaging, which captured density modulations in the system, and time-of-flight (TOF) imaging, which provided information about the global phase coherence.īy lowering the trap height quickly (in this case in just 225 ms) and then allowing the resulting atom cloud to evolve, the team was able to probe how the supersolid formed without any influence from the changing trap height. The team then lowered the barrier height (they did this at different rates in different experiments), reducing the system’s temperature further until it was low enough that the atoms condensed into a supersolid. As atoms escaped, the temperature of the remaining atoms decreased to several hundred nanokelvin. The lasers created a cigar-shaped optical barrier over which the atoms could escape if their energy was high enough. They trapped a gas of roughly 10 5 dysprosium atoms using lasers. In their experiments, the team used a technique called evaporative cooling. ![]() Ferlaino and her group now show that they can study the effect of temperature on the density modulation by obtaining a cold-atom supersolid directly from a thermal gas. This route to making a supersolid, however, has a number of issues that restrict the study of finite temperature effects. Using this method, supersolid phases have been achieved in cold-atoms that were intially superfluids-the density modulation added the solid behavior. Typically, the supersolid phase is achieved by quenching the magnitude of the short-range interaction, which induces a density modulation on top of the system’s already existing superfluid phase. The properties of a dipolar BEC are governed by short-range repulsive interactions and by long-range dipole-dipole interactions between atoms. Cold-atom physcists have shown that they can manipulate interactions to generate a supersolid starting from a cold-atom setup, specifically a dipolar Bose-Einstein condensate (BEC). Cold atoms offer an ideal environment in which to create supersolids, as researchers can engineer their atom-atom interactions in a controlled manner. Īn ensemble of cold atoms is one alternative system. Lacking unambiguous success, researchers started looking for alternative systems to obtain a supersolid. The first experiments focused on realizing supersolidity in helium, with researchers trying to move a helium sample from a solid, crystalline state to a supersolid one. The existence of a supersolid state was first proposed in 1957, long before experimentalists knew how to achieve it. The results suggest that temperature plays a definitive role in the appearance of supersolidity. Now, a team led by Francesca Ferlaino at the University of Innsbruck, Austria, has shown that when starting from a thermal gas, a supersolid’s crystalline and superfluid orders arrive and decay sequentually at the birth and death of a supersolid. Researchers typically make cold-atom supersolids starting from superfluid phases, leaving open the question of how supersolidity appears from other phases. This paradoxical behavior was observed in cold-atom experiments only in the last five years. The constituent particles of a supersolid form a rigid, ordered structure but can also flow without dissipating energy. Observing a supersolid-a state of matter that has both superfluid and solid properties-has been a challenge for decades. APS/ Carin Cain Figure 1: (Left to right) The solid and superfluid properties of a cold-atom supersolid emerge consecutively when a cold-atom thermal gas condenses into this phase. ![]()
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