Feng-Yang Zhang

Single-photon quantum router by two distant artificial atoms

Nowadays, the quantum router plays a key role in quantum communication and quantum networks. Here we propose a tunable single-photon routing scheme, based on quantum interference, which uses two distant artificial atoms coupling to two transmission lines. Depending on the distance between the two atoms, the collective effect will lead to destructive or constructive interference between the scattered photons. Under the standing wave condition, a single photon from the incident channel can be perfectly transmitted or redirected into another channel by the asymmetric or symmetric reflected phase shift of atoms, respectively. Therefore, we show that our router can be controlled by adjusting the detuning of the atoms and the interatomic distance, without any classical field.

Flexible two-qubit controlled phase gate in a hybrid solid-state system

We develop a theoretical scheme for creating coupling between nitrogen-vacancy (N-V) ensemble and superconducting qubit using a transmission line resonator. Through adjusting local external flux threading the superconducting qubit loop, the desired coupling between random superconducting qubit and transmission line resonator is obtained at will. Moreover, the flexible two-qubit controlled phase gate is realized. Also, our protocol might be implemented via the current experimental technology.

Realizing a SWAP gate and generating cluster states in a controllable superconducting coupling system

We propose a new controllable protocol for information transmission which is based on coupling superconducting charge qubits to a single-mode quantum transmission line. We show how to physically implement high-fidelity information transmission by controlling the external magnetic flux in this system. By choosing appropriate parameters, the cluster states can be generated. Finally, we investigate the feasibility of this protocol with present-day technology.

Nonadiabatic geometric rotation of an electron spin in a quantum dot by 2π hyperbolic secant pulses

In this paper, the geometric and dynamic phase components of overall phase induced by 2{\pi} hyperbolic secant pulses in a quantum dot is analyzed. The dependence of two phase components on the ratio of the Rabi frequency to the detuning is investigated. Numerical results indicate that only for one resonant pulse the induced overall phase is purely the geometric phase. With other values of the ratio the overall phase consists of a nonzero dynamic part. The effect of spin precession to decrease the dynamic phase is characterized and discussed by analytical and numerical techniques. Utilizing the symmetry relations of the phases, a scheme to eliminate the dynamic phase by multipulse control is proposed. By choosing the proper parameter for each pulse, the dynamic phases induced by different pulses cancel out. The total pure geometric phase varies from -{\pi} to {\pi}, which realizes the arbitrary geometric rotation of spin. Average fidelity is calculated and the effects of magnetic field and decay of the trion state are compared and discussed. The results show the crucial role of weak magnetic field for high fidelity (above 99.3%).

Flexible and experimentally feasible shortcut to quantum Zeno dynamic passage

Abstract We propose and discuss a theoretical scheme to speed up Zeno dynamic passage by an external acceleration Hamiltonian. This scheme is a flexible and experimentally feasible acceleration because the acceleration Hamiltonian does not adhere rigidly to an invariant relationship, whereas it can be a more general form ∑ u j ( t ) H c j . Here H c j can be arbitrarily selected without any limitation, and therefore one can always construct an acceleration Hamiltonian by only using realizable H c j . Applying our scheme, we finally design an experimentally feasible Hamiltonian as an example to speed up an entanglement preparation passage.

Long-distance quantum information transfer with strong coupling hybrid solid system

In this paper, we demonstrate how information can be transferred among the long-distance memory units in a hybrid solid architecture, which consists the nitrogen-vacancy (NV) ensemble acting as the memory unit, the LC circuit acting as the transmitter (receiver), and the flux qubit acting as the interface. Numerical simulation demonstrates that the high-fidelity quantum information transfer between memory unit and transmitter (receiver) can be implemented, and this process is robust to both the LC circuit decay and NV ensemble spontaneous emission.

Simply quantum information processing with RF superconducting qubit

Utilizing rf superconducting quantum interference devices coupled with transmission line resonator, we propose a scheme to implementing quantum information processing. In this system, the high fidelity two-qubit maximally entangled states and quantum logic gate are realized. Under the large detuning condition, the excited state of an rf superconducting quantum interference device is adiabatically eliminated. So the excited state spontaneous emission of the superconducting qubit can be effectively avoided in this paper. At last, the experimental feasibility and the challenge of our schemes have been discussed.

One-step preparation of three-particle Greenberger–Horne–Zeilinger states in cavity quantum electrodynamics

We propose two schemes to one-step generate the three-particle Greenberger–Horne–Zeilinger state based on the resonant atom–cavity fields interaction. The whole process may be realized experimentally providing that simple apparatus, initial conditions, and some manipulation in principle are achieved. Finally, in the current or the near future experiment parameter, we show that the proposed schemes can maintain the state with high fidelity under the condition of atomic spontaneous emission and decay of cavity fields.