### Session A16: Quantum Fermi Gases and Feshbach Resonances

8:00 AM–11:00 AM, Monday, March 16, 2009
Room: 317

Chair: Martin Zwierlein, Massachusetts Institute of Technology

Abstract ID: BAPS.2009.MAR.A16.12

### Abstract: A16.00012 : A study of momentum entanglement and negativity in Bardeen-Cooper-Schrieffer states at finite temperature

10:12 AM–10:24 AM

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#### Authors:

Chun KIt Chung
(Department of Physics and Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China)

Chi Kwong Law
(Department of Physics and Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China)

We study the momentum entanglement between the spin-up and spin- down particles of the homogeneous Bardeen-Cooper-Schrieffer (BCS) state at finite temperature. To achieve this, we construct from the BCS state the partial transposition $\rho_2^{\mathrm{T} _A}$ of the two particle density matrix in momentum space. The structure of $\rho_2^{\mathrm{T}_A}$ and its corresponding negativity ${\cal N}_2$ are examined. We show that $\rho_2^ {\mathrm{T}_A}$ consists of infinitely many decoupled $2 \times 2$ submatrices, and momentum entanglement coexists with the pairing order parameter $\Delta$. It is found that pairs with momenta slightly above a surface related to the Fermi energy contribute this entanglement most significantly. We propose an entanglement witness operator as a measurable quantity to detect momentum entanglement in BCS states.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.MAR.A16.12