The entanglement of two atoms is studied when the two atoms are coupled to a single-mode thermal field with different couplings. The different couplings of two atoms are in favor of entanglement preparation: it not only makes the case of absence entanglement with same coupling appear entanglement, but also enhances the entanglement with the increasing of the relative difference of two couplings. We also show that the diversity of coupling can improved the critical temperature. If the optical cavity is leaky during the time evolution, the dissipative thermal environment is benefit to produce the entanglement.
We propose a Bell measurement free scheme to implement a quantum repeater in GaAs/AlGaAs double quantum dot systems. We prove that four pairs of double quantum dots compose an entanglement unit, given that the initial state is singlet states. Our scheme differs from the famous Duan-Lukin-Cirac-Zoller (DLCZ) protocol in that the Bell measurements are unnecessary for the entanglement swapping, which provides great advantages and conveniences in experimental implementations. Our scheme significantly improves the success probability of quantum repeaters based on solid state quantum devices.
Dynamical decoupling (DD) is an active and effective method for suppressing decoherence of a quantum system from its environment. In contrast to the nominal biaxial DD, this work presents a uniaxial decoupling protocol that requires a significantly reduced number of pulses and a much lower bias field satisfying the "magic" condition. We show this uniaxial DD protocol works effectively in a number of model systems of practical interests, e.g., a spinor atomic Bose-Einstein condensate in stray magnetic fields (classical noise), or an electron spin coupled to nuclear spins (quantum noise) in a semiconductor quantum dot. It requires only half the number of control pulses and a 10-100 times lower bias field for decoupling as normally employed in the above mentioned illustrative examples, and the overall efficacy is robust against rotation errors of the control pulses. The uniaxial DD protocol we propose shines new light on coherent controls in quantum computing and quantum information processing, quantum metrology, and low field nuclear magnetic resonance.Introduction.-Decoherence, due to coupling of a system to its surrounding environment, is a key obstacle towards practical applications of quantum technologies [1][2][3]. Reliable quantum operations cannot proceed effectively or coherently without the decoherence of a quantum state under control [4]. One may naively hope for the existence of a system perfectly isolated from its environment. However, this imposes heavy resource requirement and extreme conditions, such as ultralow temperature, ultrahigh vacuum, ultraweak/ultrastrong magnetic fields [5][6][7], etc, some of which for all practical reasons cannot be achieved. Alternatively, one can search for strategies capable of slowing down or suppressing decoherence.
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