Study Of Applying Hybrid Quantum Systems For Quantum Information Processing

Quantum information science is a subject which takes advantage of quantum laws toimplement information processing, and has important application values in the field ofcomputation, communication and so on. However，the physical implementations ofquantum information processing are facing huge challenges since the existing quantumphycial systems can not be able to fulfill all these requirements for implementingquantum information processing. In recent years, a new research idea was beingproposed which is ultilizing the hybrid quantum systems and make the componentsystems complement and benefit each other. The thesis mainly studies on new schemesfor implementing quantum information processing with hybrid quantum systems. Themain results and the creative points are as follows.We present a scheme for preparing three-photon polarization-entangled W states.The signal photons and a strong probe field interact via weak cross-Kerr nonlinearitythat conditionally causes a phase shift on the probe coherent state. A W state is thenprepared with a high success probability by the homodyne measurement andpostselection. Compared with preparing photonic W states via parametric downconversion, the scheme has the characters with high success probability and norequirement for single photon detection.Various quantum repeater schemes are crucial for realizing long-distance quantumcommunication, and the hybrid systems consisting of ‘static’ quantum systems (atomicensembles) and ‘flying’ quantum system (photons) have the distinguished advantages.The exsiting quantum repeater schemes seriously depend on the stability of polarizationstates of the photons, while there are random noises in the real channels where it is veryhard to maintain the stability of polarization states. We propose a quantum repeaterscheme which is robust against polarization noise of photons transmitted overlong-distance channel. We introduce time-bin photonic states and adjust the two-photoninterference configuration and the detection way, which make the disturbed signals beeliminated, so the fidelity of distributing entanglement is not affected. Our scheme alsois robust against channel loss and channel length fluctuations. Our scheme can beperformed with current experimental setups through making some simple adjustments,and is promsing for constructing practical quantum repeater.With the development of fabrication and cooling techniques, nanomechanicalresonators recently have been made to quantum ground states and applied in quantuminformation science. We propose a scheme to realize strong coupling between atomicqubit and superconducting qubit via a nanomechanical resonator. The coupling of theatom to the nanomechancial resonator is achieved via the electric field created by thevibratons and by exciting the atom into Rydberg states. The scheme can be used to implementing quantum state transfer between atomic qubit and superconducting qubit,and construct a hybrid system consisting of the fast quantum manipulated part(superconducting qubit) and the long-information-storage time part (atomic qubit).We propose a scheme to achieve strong coupling between a transmission lineresonator (TLR) and an individual electronic spin qubit (EQ) via a nanomechanicalresonator (NAMR). Both the NAMR-TLR and the NAMR-EQ reach the strongcoupling regime, and the coupling strengthes can be controlled by adjusting externalparameters. Compared with a direct coupling between a EQ and a TLR, the achievedcoupling can be stronger. Compared with the SCQ-mediated systems for realizingTLR-EQ effective coupling, the NAMR as a mediator has a longer coherence time. Thecontrollable strong couplings achived in the scheme be used to implement ahigh-fidelity quantum state transfer between the spin qubit and the TLR.