Yi-Hao Kang

Fast preparation of W states with superconducting quantum interference devices by using dressed states

In this paper, we propose a protocol to prepare W states with superconducting quantum interference devices (SQUID) by using dressed states. Through choosing a set of dressed states suitably, the protocol can be used to accelerate the adiabatic passages while additional couplings are unnecessary. Moreover, we can optimize the evolution of the system with the restraint to the populations of the intermediate states by choosing suitable controlled parameters. Numerical simulations show that the protocol is robust against the parameter variations and decoherence mechanisms. Furthermore, the protocol is faster and more robust against the dephasing, compared with that by the adiabatic passages. As for the Rabi frequencies of pulses designed by the method, they can be expressed by the linear superpositions of Gaussian functions, which does not increase difficulties to the experiments. In addition, the protocol could be controlled and manipulated easily in experiments with a circuit quantum electrodynamics system.

Complete Bell-state analysis for superconducting-quantum-interference-device qubits with a transitionless tracking algorithm

In this paper, we propose a protocol for complete Bell-state analysis for two superconducting-quantum-interference-device qubits. The Bell-state analysis could be completed by using a sequence of microwave pulses designed by the transition- less tracking algorithm, which is an useful method in the technique of shortcut to adiabaticity. After the whole process, the information for distinguishing four Bell states will be encoded on two auxiliary qubits, while the Bell states keep unchanged. One can read out the information by detecting the auxiliary qubits. Thus the Bell-state analysis is nondestructive. The numerical simulations show that the protocol possesses high success probability of distinguishing each Bell state with current experimental technology even when decoherence is taken into account. Thus, the protocol may have potential applications for the information readout in quantum communications and quantum computations in superconducting quantum networks.

Reverse engineering of a Hamiltonian by designing the evolution operators.

We propose an effective and flexible scheme for reverse engineering of a Hamiltonian by designing the evolution operators to eliminate the terms of Hamiltonian which are hard to be realized in practice. Different from transitionless quantum driving (TQD), the present scheme is focus on only one or parts of moving states in a D-dimension (D ≥ 3) system. The numerical simulation shows that the present scheme not only contains the results of TQD, but also has more free parameters, which make this scheme more flexible. An example is given by using this scheme to realize the population transfer for a Rydberg atom. The influences of various decoherence processes are discussed by numerical simulation and the result shows that the scheme is fast and robust against the decoherence and operational imperfection. Therefore, this scheme may be used to construct a Hamiltonian which can be realized in experiments.

Fast quantum state engineering via universal SU(2) transformation

We introduce a simple yet versatile protocol to inverse engineer the time-dependent Hamiltonian in two- and three level systems. In the protocol, by utilizing a universal SU(2) transformation, a given speedup goal can be obtained with large freedom to select the control parameters. As an illustration example, the protocol is applied to perform population transfer between nitrogen-vacancy (NV) centers in diamond. Numerical simulation shows that the speed of the present protocol is fast compared with that of the adiabatic process. Moreover, the protocol is also tolerant to decoherence and experimental parameter fluctuations. Therefore, the protocol may be useful for designing an experimental feasible Hamiltonian to engineer a quantum system.

Fast generation of W states of superconducting qubits with multiple Schrödinger dynamics

In this paper, we present a protocol to generate a W state of three superconducting qubits (SQs) by using multiple Schrödinger dynamics. The three SQs are respective embedded in three different coplanar waveguide resonators (CPWRs), which are coupled to a superconducting coupler (SCC) qubit at the center of the setups. With the multiple Schrödinger dynamics, we build a shortcuts to adiabaticity (STA), which greatly accelerates the evolution of the system. The Rabi frequencies of the laser pulses being designed can be expressed by the superpositions of Gaussian functions via the curves fitting, so that they can be realized easily in experiments. What is more, numerical simulation result shows that the protocol is robust against control parameters variations and decoherence mechanisms, such as the dissipations from the CPWRs and the energy relaxation. In addition, the influences of the dephasing are also resisted on account of the accelerating for the dynamics. Thus, the performance of the protocol is much better than that with the conventional adiabatic passage techniques when the dephasing is taken into account. We hope the protocol could be implemented easily in experiments with current technology.

Complete polarized photons Bell-states and Greenberger–Horne–Zeilinger-states analysis assisted by atoms

We propose an efficient protocol for complete polarized photons Bell-states and Greenberger–Horne–Zeilinger (GHZ)-states analysis assisted by atoms. With the help of assistant atoms and some simple liner optical elements, the analysis of both polarization Bell states and GHZ states can be performed completely. In our protocol, the assistant atoms are trapped in cavity quantum electronic dynamics (QED), which is feasible with current experimental technology. Moreover, the polarized photons entangled states will not be destroyed in our protocol. Therefore, our scheme might contribute to the quantum communication, quantum computation, and some other fields in quantum information processing.

Invariant-Based Pulse Design for Three-Level Systems Without the Rotating-Wave Approximation

In this paper, a scheme is put forward to design pulses which drive a three-level system based on the reverse engineering with Lewis-Riesenfeld invariant theory. The scheme can be applied to a three-level system even when the rotating-wave approximation (RWA) can not be used. The amplitudes of pulses and the maximal values of detunings in the system could be easily controlled by adjusting control parameters. We analyze the dynamics of the system by an invariant operator, so additional couplings are unnecessary. Moreover, the approaches to avoid singularity of pulses are studied and several useful results are obtained. We hope the scheme could contribute to fast quantum information processing without RWA.

Efficient preparation of Greenberger–Horne–Zeilinger state and W state of atoms with the help of the controlled phase flip gates in quantum nodes connected by collective-noise channels

Noise plays a troublesome role for entanglement generation, because the polarization entanglement of photons can be easily disturbed by the noise. In this paper, we propose a protocol to prepare Greenberger–Horne–Zeilinger state and W state of atoms in quantum nodes connected by collective-noise channels assisted by quantum nondemolition detectors (QNDs) and the controlled phase flip gates. The frequency degrees of freedom are exploited in our protocol. The successful probability of our protocol can reach 100% neglecting the photon loss and assuming that the efficiency of QNDs is 1. Moreover, the number of times of using QNDs is limited, and this makes the protocol quite effective when collective noise is small.

Rapid generation of a three-dimensional entangled state for two atoms trapped in a cavity via shortcuts to adiabatic passage

We present an efficient protocol to rapidly generate a three-dimensional entangled state for two atoms trapped in a cavity with quantum Zeno dynamics and Lewis–Riesenfeld invariants. The required time for the protocol is much shorter than that with adiabatic passage. The influence of various decoherence processes such as atomic spontaneous emission and photon loss on the fidelity of the three-dimensional entangled state is investigated. Numerical simulation demonstrates that the protocol is robust against both the atomic spontaneous emission and cavity decay. Different from Lin et al. (J Opt Soc Am B 33(4):519–524, 2016), the three-dimensional entangled state can be fast generated with only one step. Furthermore, the protocol can be generalized to generate N-dimensional entanglement state. Therefore, we hope the protocol may be useful in quantum information field.

Effective scheme for preparation of a spin-qubit Greenberger–Horne–Zeilinger state and W state in a quantum-dot-microcavity system

We propose a scheme for the preparation of a spin-qubit Greenberger–Horne–Zeilinger (GHZ) state and W state by using quantum dots (QDs) in double-sided optical microcavities with the help of polarized photons. The spin-selective photon reflection from the cavity provides us a perfect way to achieve the scheme by adding some simple linear optical elements and conventional photon detectors. A numerical simulation demonstrates that a perfect scheme of the GHZ state and W state generation can be achieved in one step, and high fidelities can be realized when the side leakage and cavity loss are low, which is feasible in the weak coupling regime. Therefore, our scheme might contribute to quantum communication, quantum teleportation, and some other fields in quantum information processing.