Superfluid Fermi atomic gas as a quantum simulator for the study of the neutron-star equation of state in the low-density region

Abstract

We propose a theoretical idea to use an ultracold Fermi gas as a quantum simulator for the study of the low-density region of a neutron-star interior. Our idea is different from the standard quantum simulator that heads for perfect replication of another system, such as the Hubbard model discussed in high-T c cuprates. Instead, we use the similarity between two systems and theoretically make up for the difference between them. That is, (1) we first show that the strong-coupling theory developed by Nozières and Schmitt-Rink (NSR) can quantitatively explain the recent experiment on the equation of state (EoS) in a 6 Li superfluid Fermi gas in the BCS (Bardeen-CooperSchrieffer) unitary limit far below the superfluid phase-transition temperature T c . This region is considered to be very similar to the low-density region (crust regime) of a neutron star (where a nearly unitary s-wave neutron superfluid is expected). (2) We then theoretically compensate the difference that, while the effective range r eff is negligibly small in a superfluid 6 Li Fermi gas, it cannot be ignored (r eff = 2.7 fm) in a neutron star, by extending the NSR theory to include effects of r eff . The calculated EoS when r eff = 2.7 fm is shown to agree well with the previous neutron-star EoS in the low-density region predicted in nuclear physics. Our idea indicates that an ultracold atomic gas may more flexibly be used as a quantum simulator for the study of other complicated quantum many-body systems, when we use not only the experimental high tunability, but also the recent theoretical development in this field. Since it is difficult to directly observe a neutron-star interior, our idea would provide a useful approach to the exploration for this mysterious astronomical object.

Fermi gas throughout the BCS-BEC crossover: Comparative study of t -matrix approaches with various degrees of self-consistency

“…For the (G 0 G 0 )G 0 , (G 0 G 0 )G, and (GG)G approaches we found good agreement with the data published in Refs. [12], [27], and [17], respectively. For the (15).…”

Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC crossover in a two-band Fermi gas

“…Owing to the emergence of additional degrees of freedom of the order parameter, these multi-condensate systems can lead to a plethora of novel quantum phenomena. While even the single-component fermionic condensate has bridged various research fields such as nuclear physics [12][13][14][15][16][17][18][19] and several solid-state systems 4,7,8,[20][21][22][23][24][25][26][27][28][29][30][31] , the more generic concept of multi-component BCS-BEC crossover not only builds up an interdisciplinary crosslink among strongly correlated systems but also opens a new frontier to explore the optimal configuration for high-T c superconductivity 32,33 .…”

Cold atom quantum simulator for dilute neutron matter

“…On the other hand, it has been pointed out that the effective range also decreases the internal energy by increasing the Hartree energy. 68 Since the net change of the internal energy depends on the value of the interaction parameter, the EOS shown in Fig. 7(a) cannot constrain the EOS for the internal energy density of neutron matter.…”