Below absolute zero reached in quantum gas

RAGNAR EKHOLM, Leonard D. Kohn, Seymour H. Wollman

Jelena Stajic

Quantum Gases Atomic gases can be cooled to a fraction of a degree above absolute zero and—if they are also dense enough—can enter a regime where their quantum properties come to the fore. In reaching this so-called quantum degenerate regime, particle loss through three-body collisions is usually a foe rather than a friend. Dogra et al. predict theoretically that a weakly interacting 3D gas of bosonic atoms can be made more degenerate by exploiting, rather than fighting, three-body particle loss. For the scheme to work, the gas should reside in a homogeneous trap, and the cooling must start from a particular subset of initial conditions, both of which should be realizable in the lab. Phys. Rev. Lett. 123 , 020405 (2019).

Marco Merkli

M. J. Stephen

The correlation energy of a charged Boltzmann gas at absolute zero is calculated. The result is exact at high density in the same sense as the result of Gell-Mann and Brueckner for the Fermi gas. Investigation of the magnetic properties reveals that at absolute zero this system exhibits a Meissner effect of the London type. At any finite temperature the system is diamagnetic. Consideration of the effect of the Coulomb interaction on the Meissner effect leads to the conjecture that the London constant is independent of the particle interactions. The results are also applicable to a charged boson gas at absolute zero.

Jakub Meisner

Ji-Bing Yuan, Bo Zhang, Ya‐Ju Song +3 more

We propose a theoretical scheme for quantum sensing of temperature close to absolute zero in a quasi-one-dimensional Bose-Einstein condensate (BEC). In our scheme, a single-atom impurity qubit is used as a temperature sensor. We investigate the sensitivity of the single-atom sensor in estimating the temperature of the BEC. We demonstrate that the sensitivity of the temperature sensor can saturate the quantum Cram\'er-Rao bound by means of measuring quantum coherence of the probe qubit. We study the temperature sensing performance by using quantum signal-to-noise ratio (QSNR). It is indicated that there is an optimal encoding time at which the QSNR can reach its maximum in the full-temperature regime. In particular, we find that the QSNR reaches a finite upper bound in the weak coupling regime even when the temperature is close to absolute zero, which implies that the sensing-error-divergence problem is avoided in our scheme. Our work opens a way for quantum sensing of temperature close to absolute zero in the BEC.