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Hu'nan Shifan Daxue xuebao. Ziran kexue ban

Quantum Computing with Two Artificial Atoms Coupled to a Single-mode Resonant Cavity

Xiaomei Chen

Published Jan 1, 2005• 0 citations
OpenAlex

Abstract

A small Josephson junction(a artificial atom) coupled to a resonant cavity is expounded,we show the Hamiltonian of the junction-cavity system.Then,under some conditions,we obtain the simplified form of the Hamiltonian.Finally,we propose a quantum computing scheme of two artificial atoms coupled to a single-mode resonant cavity,which performs a control-NOT gate.

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Chinese Journal of Quantum Electronics•Jan 1, 2006•0 citations
A small Josephson junction(a artificial atom) coupled to a resonant cavity is expounded,we show the Hamiltonian of the junction-cavity system.Then,under some conditions,we obtain the simplified form of the Hamiltonian.Finally,we propose a quantum computing scheme of two artificial atoms coupled to a single-mode resonant cavity,which performs a control-NOT gate.
We present a quantum computing scheme with atomic Josephson junction arrays. The system consists of a small number of atoms with three internal states and trapped in a far-off-resonant optical lattice. Raman lasers provide the ``Josephson'' tunneling, and the collision interaction between atoms represent the ``capacitive'' couplings between the modes. The qubit states are collective states of the atoms with opposite persistent currents. This system is closely analogous to the superconducting flux qubit. Single-qubit quantum logic gates are performed by modulating the Raman couplings, while two-qubit gates result from a tunnel coupling between neighboring wells. Readout is achieved by tuning the Raman coupling adiabatically between the Josephson regime to the Rabi regime, followed by a detection of atoms in internal electronic states. Decoherence mechanisms are studied in detail promising a high ratio between the decoherence time and the gate operation time.
We carry out a quantum-mechanical analysis of a small Josephson junction coupled to a single-mode resonant cavity. We find that the eigenstates of the combined junction-cavity system are strongly entangled only when the gate voltage applied at one of the superconducting islands is tuned to certain special values. One such value corresponds to the resonant absorption of a single photon by Cooper pairs in the junction. Another special value corresponds to a two-photon absorption process. Near the single-photon resonant absorption, the system is accurately described by a simplified model in which only the lowest two levels of the Josephson junction are retained in the Hamiltonian matrix. We noticed that this approximation does not work very well as the number of photons in the resonator increases. Our system shows also the phenomenon of ``collapse and revival'' under suitable initial conditions, and our full numerical solution agrees with the two level approximation result.
Josephson junctions have been shown to be a promising solid-state system for implementation of quantum computation. The two-qubit gates are generally realized by the capacitive coupling between the nearest-neighbor qubits. We propose an effective Hamiltonian to describe charge qubits coupled through the microwave cavity. We find that nontrivial two-qubit gates may be achieved by this coupling. The ability to interconvert localized charge qubits and flying qubits in the proposed scheme implies that quantum network can be constructed using this large scalable solid-state system.
In this paper we propose a Hamiltonian generalizing the interaction of the two--level atom and both the single radiation mode and external field ......... a kind of cavity QED. We solve the Schrodinger equation in the strong coupling regime by making use of rotating wave approximation under new resonance conditions containing the Bessel functions and etc, and obtain unitary transformations of four types corresponding to Rabi oscillations which perform quantum logic gates in Quantum Computation.
We present a model for quantum computation using nnn steady 3-level atoms kept inside a quantum cavity, or using nnn quantum-dots (QDs) kept inside a quantum cavity. In this model one external laser is pointed towards all the atoms/QDs, and nnn pairs of electrodes are addressing the atoms/QDs, so that each atom is addressed by one pair. The energy levels of each atom/QD are controlled by an external Stark field given to the atom/QD by its external pair of electrodes. Transition between two energy levels of an individual atom/ QD are controlled by the voltage on its electrodes, and by the external laser. Interactions between two atoms/ QDs are performed with the additional help of the cavity mode (using on-resonance condition). Laser frequency, cavity frequency, and energy levels are far off-resonance most of the time, and they are brought to the resonance (using the Stark effect) only at the time of operations. Steps for a controlled-NOT gate between any two atoms/QDs have been described for this model. Our model demands some challenging technological efforts, such as manufacturing single-electron QDs inside a cavity. However, it promises big advantages over other existing models which are currently implemented, and might enable a much easier scale-up, to compute with many more qubits.
Any quantum computation can be simplified to a gate sequence. But the quantum computation is carried out by a certain physical system. We propose here a scheme to carry out two-atom quantum controlled phase gate through cavity QED. In our scheme, the atomic transition is largely detuned with the cavity mode of interest, so the atomic spontaneous emission loss is strongly suppressed, and this leads to the enhancement of probability of gate operation. But fidelity is decided by constantsα,β,γ. The numerical calculation based on current experimental technology shows that our scheme has high gate fidelity, the average value of fidelity F = 0.982318. That scheme can be realized by experiment.