Many-qubit network employing cavity QED in a decoherence-free subspace (original) (raw)
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Scalable quantum computation with cavity QED systems
Physical Review A, 2000
We propose a scheme for quantum computing using high-Q cavities in which the qubits are represented by single cavity modes restricted in the space spanned by the two lowest Fock states. We show that single qubit operations and universal multiple qubit gates can be implemented using atoms sequentially crossing the cavities.
Lobachevskii Journal of Mathematics, 2013
We propose an effective realization of the universal set of elementary quantum gates in solid state quantum computer based on macroscopic (or mesoscopic) resonance systems -multi-atomic coherent ensembles, squids or quantum dots in quantum electrodynamic cavity. We exploit an encoding of logical qubits by the pairs of the macroscopic two-or three-level atoms that is working in a Hilbert subspace of all states inherent to these atomic systems. In this subspace, logical single qubit gates are realized by the controlled reversible transfer of single atomic excitation in the pair via the exchange of virtual photons and by the frequency shift of one of the atomic ensembles in a pair. In the case of two-level systems, the logical two-qubit gates are performed by the controlling of Lamb shift magnitude in one atomic ensemble, allowing/blocking the excitation transfer in a pair, respectively, that is controlled by the third atomic system of another pair. When using threelevel systems, we describe the NOT-gate in the atomic pair controlled by the transfer of working atomic excitation to the additional third level caused by direct impact of the control pair excitation. Finally, we discuss advantages of the proposed physical system for accelerated computation of some useful quantum gates.
Implementing universal quantum gates in coupled cavities
Arxiv preprint arXiv:0707.3946, 2007
Abstract: We study a linear array of coupled cavities interacting with two level systems and show how to construct individually addressable qubits in this system from the long-lived atom-photon excitations (polaritons) at each site. We derive the system dynamics and show that is described by an XY Hamiltonian. We proceed by showing how to implement non-local quantum gates and show that combined with the inherent ability for individual addressing, universal quantum computation is possible in this system. We finally discuss the prospects ...
Coherent Operation of a Tunable Quantum Phase Gate in Cavity QED
Physical Review Letters, 1999
We have realized a quantum phase gate operating on quantum bits carried by a single Rydberg atom and a zero-or one-photon field in a high-Q cavity. The gate operation is based on the dephasing of the atom-field state produced by a full cycle of quantum Rabi oscillation. The dephasing angle, conditioned to the initial atom-field state, can be adjusted over a wide range by tuning the atom-cavity frequency difference. We demonstrate that the gate preserves qubit coherence and generates entanglement. This gate is an essential tool for the nondestructive measurement of single photons and for the manipulation of many-qubit entanglement in cavity QED. PACS numbers: 03.67.Lx, 32.80.Rm, 42.50.Ar Entanglement is a most striking feature of quantum theory. Its puzzling implications have motivated an intense theoretical and experimental research work. It has been proposed to make use of many entangled two-level quantum systems (qubits) to implement new information processing functions [1]. These applications require the production of complex entangled states. Such manipulations can be decomposed into a sequence of simple unitary evolutions, involving one or two qubits, performed by quantum gates.
Realization of quantum gates with multiple control qubits or multiple target qubits in a cavity
2012
We propose a scheme to realize a three-qubit controlled phase-gate and a multi-qubit controlled-NOT gate of one qubit simultaneously controlling n target qubits with a four-level quantum system in a cavity. The implementation time for multi-qubit controlled NOT gate is independent of number of qubit. Three-qubit phase-gate is generalized to n-qubit phase-gate with multiple control qubits. The number of steps reduces linearly as compared to conventional gate decomposition method. Our scheme can be applied to various types of physical systems such as superconducting qubits coupled to a resonator and trapped atoms in a cavity. Our scheme does not require adjustment of level spacing during the gate implementation. We also show the implementation of Deutsch-Joza algorithm. Finally, we discuss the imperfections due to cavity decay and the possibility of physical implementation of our scheme.
Heralded quantum entangling gate for distributed quantum computation in a decoherence-free subspace
arXiv (Cornell University), 2023
We propose a heralded nonlocal protocol for implementing an entangling gate on two stationary qubits coupled to spatially separated cavities. By dynamically controlling the evolution of the composite system, the entangling gate can be achieved without real excitations of cavity modes nor atoms. The success of our protocol is conditioned on projecting an auxiliary atom onto a postselected state, which simultaneously removes various detrimental effects of dissipation on the gate fidelity. In principle, the success probability of the gate can approach unity as the single-atom cooperativity becomes sufficiently large. Furthermore, we show its application for implementing single-and twoqubit gates within a decoherence-free subspace that is immune to a collective dephasing noise. This heralded, faithful, and nonlocal entangling gate protocol can, therefore, be useful for distributed quantum computation and scalable quantum networks.
Cavity-based architecture to preserve quantum coherence and entanglement
2015
Quantum technology relies on the utilization of resources, like quantum coherence and entanglement, which allow quantum information and computation processing. This achievement is however jeopardized by the detrimental effects of the environment surrounding any quantum system, so that finding strategies to protect quantum resources is essential. Non-Markovian and structured environments are useful tools to this aim. Here we show how a simple environmental architecture made of two coupled lossy cavities enables a switch between Markovian and non-Markovian regimes for the dynamics of a qubit embedded in one of the cavity. Furthermore, qubit coherence can be indefinitely preserved if the cavity without qubit is perfect. We then focus on entanglement control of two independent qubits locally subject to such an engineered environment and discuss its feasibility in the framework of circuit quantum electrodynamics. With up-to-date experimental parameters, we show that our architecture allo...
Geometric entangling gates for coupled cavity system in decoherence-free subspaces
Optics Communications, 2012
We propose a scheme to implement geometric entangling gates for two logical qubits in a coupled cavity system in decoherence-free subspaces. Each logical qubit is encoded with two atoms trapped in a single cavity and the geometric entangling gates are achieved by cavity coupling and controlling the external classical laser fields. Based on the coupled cavity system, the scheme allows the scalability for quantum computing and relaxes the requirement for individually addressing atoms.
A CNOT gate between multiphoton qubits encoded in two cavities
Nature Communications, 2018
Entangling gates between qubits are a crucial component for performing algorithms in quantum computers. However, any quantum algorithm must ultimately operate on error-protected logical qubits encoded in high-dimensional systems. Typically, logical qubits are encoded in multiple two-level systems, but entangling gates operating on such qubits are highly complex and have not yet been demonstrated. Here we realize a controlled NOT (CNOT) gate between two multiphoton qubits in two microwave cavities. In this approach, we encode a qubit in the high-dimensional space of a single cavity mode, rather than in multiple two-level systems. We couple two such encoded qubits together through a transmon, which is driven by an RF pump to apply the gate within 190 ns. This is two orders of magnitude shorter than the decoherence time of the transmon, enabling a high-fidelity gate operation. These results are an important step towards universal algorithms on error-corrected logical qubits.
Quantum computing without qubit-qubit interactions
2005
Quantum computing tries to exploit entanglement and interference to process information more efficiently than the best known classical solutions. Experiments demonstrating the feasibility of this approach have already been performed. However, finding a really scalable and robust quantum computing architecture remains a challenge for both, experimentalists and theoreticians. In most setups decoherence becomes non-negligible when one tries to perform entangling gate operations using the coherent control of qubit-qubit interactions. However, in this proceedings we show that two-qubit gate operations can be implemented even without qubit-qubit interactions and review a recent quantum computing scheme by Lim et al. [Phys. Rev. Lett. 95, 030505 (2005)] using only single photon sources (e.g. atom-cavity systems, NV colour centres or quantum dots) and photon pair measurements.