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arXiv:quant-ph/0401058

Two-Qubits Entanglement Induced by a Faster Data Bus

P. Zhang, Y. D. Wang, C. P. Sun

Published Jan 11, 2004• 0 citations
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Abstract

We propose a theoretical protocol to create the entanglement of two qubits via the Born-Oppenheimer (BO) approximation. In our scheme, each qubit is coupled to a faster data bus whose frequency is much larger than the energy spacing of the qubits and thus the BO approximation is valid. Then the adiabatic separation of qubits from the data bus can induce an effective potential to couple the two qubits, which can be utilized to create a quantum logic gate. We also discuss the quantum decoherence caused by the adiabatic entanglement between the two qubits and the external field.

DOI
10.48550/arxiv.quant-ph/0401058

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We propose a theoretical protocol to create the entanglement of two qubits via the Born-Oppenheimer (BO) approximation. In our scheme, each qubit is coupled to a faster data bus whose frequency is much larger than the energy spacing of the qubits and thus the BO approximation is valid. Then the adiabatic separation of qubits from the data bus can induce an effective potential to couple the two qubits, which can be utilized to create a quantum logic gate. We also discuss the quantum decoherence caused by the adiabatic entanglement between the two qubits and the external field.
We revisit the protocols to create maximally entangled states between two Josephson junction (JJ) charge phase qubits coupled to a microwave field in a cavity as a quantum data bus. We analyze a novel mechanism of quantum decoherence due to the adiabatic entanglement between qubits and the data bus, the off-resonance microwave field. We show that even if the variable of the data bus can be adiabatically eliminated, the entanglement between the qubits and data bus remains and can decohere the superposition of two-particle state. Fortunately we can construct a decoherence-free subspace of two-dimension to against this adiabatic decoherence. To carry out the analytic study for this decoherence problem, we develop Fröhlich transformation to re-derive the effective Hamiltonian of these systems, which is equivalent to that obtained from the adiabatic elimination approach.
We propose a theoretical protocol for quantum logic gates between two Josephson junction charge-phase qubits through the control of their coupling to a large junction whose Josephson coupling energy is much larger than its Coulomb charge energy. In the low excitation limit of the large junction, it behaves effectively as a quantum data-bus mode of a harmonic oscillator. Our protocol can be fast since it does not require the data-bus to stay adiabatically in its ground state, as such it can be implemented over a wide parameter regime independent of the data-bus quantum state.
We revisit the protocols to create maximally entangled states between two Josephson junction (JJ) charge phase qubits coupled to a microwave field in a cavity as a quantum data bus. We devote to analyze a novel mechanism of quantum decoherence due to the adiabatic entanglement between qubits and the data bus, the off-resonance microwave field. We show that even through the variable of the data bus can be adiabatically eliminated, the entanglement between the qubits and data bus remains and can decoher the superposition of two-particle state. Fortunately we can construct a decoherence-free subspace of two-dimension to against this adiabatic decoherence.To carry out the analytic study for this decoherence problem, we develop Frőhlich transformation to re-derive the effective Hamiltonian of these system, which is equivalent to that obtained from the adiabatic elimination approach .
Abstract The optimal generation of entangled states is of significance to information processing and state engineering. Here, an efficient scheme is proposed for creating entangled states between two superconducting qubits in a circuit quantum electrodynamics (QED). The two qubits that resonantly interact with a common cavity mode of transmission‐line resonator (TLR) can be effectively coupled by the data bus of the microwave resonator. By the invariant‐based shortcuts to adiabaticity (STA), two types of maximally entangled states can be controllably induced only by adjusting the Rabi drivings. Based on the resonant drivings with constant rates, the shortcut strategy is capable of implementing faster operations when compared with the dispersive approach. The fidelities are highly robust against the decoherence effects and the instabilities of Rabi rates. Thus the proposal could offer a potential route toward the entanglement generations in an optimized manner.
We study a system of two qubits interacting with a common environment, described by a two-spin boson model. We demonstrate two competing roles of the environment: inducing entanglement between the two qubits and making them decoherent. For the environment of a single harmonic oscillator, if its frequency is commensurate with the induced two-qubit coupling strength, the two qubits could be maximally entangled and the environment could be separable. In the case of the environment of a bosonic bath, the gap of its spectral density function is essential to generate entanglement between two qubits at equilibrium and for it to be used as a quantum data bus.
The power of a quantum circuit is determined through the number of two-qubit entangling gates that can be performed within the coherence time of the system. In the absence of parallel quantum gate operations, this would make the quantum simulators limited to shallow circuits. Here, we propose a protocol to parallelize the implementation of two-qubit entangling gates between multiple users which are spatially separated, and use a commonly shared spin chain data-bus. Our protocol works through inducing effective interaction between each pair of qubits without disturbing the others, therefore, it increases the rate of gate operations without creating crosstalk. This is achieved by tuning the Hamiltonian parameters appropriately, described in the form of two different strategies. The tuning of the parameters makes different bilocalized eigenstates responsible for the realization of the entangling gates between different pairs of distant qubits. Remarkably, the performance of our protocol is robust against increasing the length of the data-bus and the number of users. Moreover, we show that this protocol can tolerate various types of disorders and is applicable in the context of superconductor-based systems. The proposed protocol can serve for realizing two-way quantum communication.