Thermal blurring of a coherent Fermi gas
نویسندگان
چکیده
It is generally assumed that a condensate of paired fermions at equilibrium is characterized by a macroscopic wavefunction with a well-defined, immutable phase. In reality, all systems have a finite size and are prepared at non-zero temperature; the condensate has then a finite coherence time, even when the system is isolated in its evolution and the particle number N is fixed. The loss of phase memory is due to interactions of the condensate with the excited modes that constitute a dephasing environment. This fundamental effect, crucial for applications using the condensate of pairs’ macroscopic coherence, was scarcely studied. We link the coherence time to the condensate phase dynamics, and we show with a microscopic theory that the time derivative of the condensate phase operator θ̂0 is proportional to a chemical potential operator that we construct including both the pair-breaking and pair-motion excitation branches. In a single realization of energy E, θ̂0 evolves at long times as −2μmc(E)t/~where μmc(E) is the microcanonical chemical potential; energy fluctuations from one realization to the other then lead to a ballistic spreading of the phase and to a Gaussian decay of the temporal coherence function with a characteristic time ∝ N1/2. In the absence of energy fluctuations, the coherence time scales as N due to the diffusive motion of θ̂0. We propose a method to measure the coherence time with ultracold atoms, which we predict to be tens of milliseconds for the canonical ensemble unitary Fermi gas.
منابع مشابه
Finite temperature dynamic structure function of the free Fermi gas
A detailed discussion of the coherent and incoherent dynamic structure function of the free Fermi gas at finite temperature is presented. Their behavior and evolution with the momentum transfer and the temperature is analyzed, while particular attention is paid to the way in which their relative contribution changes with respect to the˜T = 0 case. The influence of thermal effects on the lowest ...
متن کاملRelaxation and Thermal Conductivity of Hot and Thermal Quasiparticles and Fermi Liquid Interactions in d-wave Superconductors
In this paper, we calculate theoretically the relaxation rates of hot, thermal and antinodal quasiparticles by using Fermi’s golden rule. The transition probabilities at low temperatures express in terms of Bogoliubov coefficients, singlet and triplet scattering amplitudes and dimensionless Landau parameters. The values of Landau parameters may be determined by comparison with the experimental ...
متن کاملObservation of Fermi pressure in a gas of trapped atoms.
We report the attainment of simultaneous quantum degeneracy in a mixed gas of bosons (lithium-7) and fermions (lithium-6). The Fermi gas has been cooled to a temperature of 0.25 times the Fermi temperature by thermal collisions with the evaporatively cooled bosons. At this temperature, the spatial size of the gas is strongly affected by the Fermi pressure resulting from the Pauli exclusion prin...
متن کاملThe impact of thermal gas in AGN jets on the low - frequency emission
We study the effect of non-relativistic, thermal matter in the jets of active galaxies (AGN) on the low-frequency non-thermal emission and the variability thereof. In matter-dominated jets, sizable quantities of gas should exist, in particular in the compression zones near the collision fronts that are an implicit ingredient of Fermi-type particle acceleration scenarios. Non-relativistic therma...
متن کامل