University of North Dakota Faculty/Staff Newsletter

Physics colloquium is Feb. 19

Physics will host a colloquium at 4 p.m. Friday, Feb. 19, in 211 Witmer Hall featuring Jian Wei, physics and Astronomy, Northwestern University. Coffee and cookies will be served at 4 p.m. in 215 Witmer Hall.

Abstract: Nonlocal entanglement is crucial for quantum information processes. While nonlocal entanglement has been realized for photons, it is much more difficult to demonstrate for electrons. One approach that has been proposed is to use hybrid superconducting/normal-metal devices. When the distance between two normal-metal electrodes connected to a superconductor is comparable to the superconducting coherence length, theory predicts that two electrons in the normal-metal electrodes with opposite spin are entangled by Cooper pairs, leading to non-local entanglement of electrons. Such entanglement can be understood by a non-local process called crossed Andreev reflection (CAR), in which a Cooper pair splits into two coherent electrons with one in each normal-metal electrode, generating instantaneous current of the same sign and inducing a positive current correlation.

Using both nonlocal resistance measurements and cross-correlation measurements, we find very convincing experimental evidence of such nonlocal entanglement. Moreover, by controlling the energy of electrons at the superconductor/normal-metal interfaces, we find that the amplitude of such entanglement can be maximized, in agreement with theoretical predication.

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