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arXiv:0908.3308 · Europhysics Letters (EPL)

A single-interaction step implementation of a quantum search in coupled micro-cavities

Elica S. Kyoseva, Dimitris G. Angelakis, L. C. Kwek

Published Jan 1, 2010• 11 citations
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Abstract

We present a method for realizing efficiently Grover's search algorithm in an array of coupled cavities doped with three-level atoms. We show that by encoding information in the lowest two ground states of the dopants and through the application of appropriately tuned global laser fields, the reflection operator needed for the quantum search algorithm can be realized in a single physical operation. Thus, the time steps in which Grover's search can be implemented become equal to the mathematical steps , where N is the size of the register. We study the robustness of the implementation against errors due to photon loss and fluctuations in the cavity frequencies and atom-photon coupling constants.

DOI
10.1209/0295-5075/89/20005

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We present a method for realizing efficiently Grover's search algorithm in an array of coupled cavities doped with three-level atoms. We show that by encoding information in the lowest two ground states of the dopants and through the application of appropriately tuned global laser fields, the reflection operator needed for the quantum search algorithm can be realized in a single physical operation. Thus, the time steps in which Grover's search can be implemented become equal to the mathematical steps , where N is the size of the register. We study the robustness of the implementation against errors due to photon loss and fluctuations in the cavity frequencies and atom-photon coupling constants.
We propose an implementation of the quantum search algorithm of a marked item in an unsorted list of N items by adiabatic passage in a cavity-laser-atom system. We use an ensemble of N identical three-level atoms trapped in a single-mode cavity and driven by two lasers. In each atom, the same level represents a database entry. One of the atoms is marked by having an energy gap between its two ground states. Appropriate time delays between the two laser pulses allow one to populate the marked state starting from an initial entangled state within a decoherence-free adiabatic subspace. The time to achieve such a process is shown to exhibit the square root N Grover speedup.
Using resonant interaction of three Rydberg atoms with a single-mode microwave cavity, we consider a realization of the three-qubit Grover search algorithm in the presence of weak cavity decay, based on a previous idea for a three-qubit quantum gate [Chen et al., Phys. Rev. A 73, 064304 (2006)]. We simulate the searching process under the influence of the cavity decay and show that our scheme could be achieved efficiently to find a marked state with high fidelity. The required operations are very close to the capabilities of current cavity QED techniques.
We propose an ion-trap implementation of Grover's quantum search algorithm for an unstructured database of arbitrary length NNN. The experimental implementation is appealingly simple because the linear ion trap allows for a straightforward construction, in a single interaction step and without a multitude of Hadamard transforms, of the reflection operator, which is the engine of the Grover algorithm. Consequently, a dramatic reduction in the number of the required physical steps takes place, to just O(N)O(\sqrt{N})O(N​), the same as the number of mathematical steps. The proposed setup allows for demonstration of both the original (probabilistic) Grover search and its deterministic variation, and is remarkably robust to imperfections in the register initialization.
Abstract This work concerns a three-qubit processor implemented as three transmon-type superconducting qubits capacitively coupled to a superconducting resonator driven by a microwave field. Based on an effective Hamiltonian of this system, we propose a scheme to realize an X -rotation gate for three qubits requiring only a single-step operation. During the gate operation, the cavity photon-number is canceled due to the strong microwave field. It does not require the cavity to be initially in the vacuum state and the scheme is insensitive to cavity decay. We also present an effective scheme to implement Grover’s search algorithm based on this quantum gate and a phase oracle. Using numerical simulation and analysis, we show that the proposed schemes allow for efficiently finding the target state with a high fidelity. The potential application of these proposals with current QED circuit technology is also discussed.
We show that iteration of a few ( ∼N1/4\sim N^{1/4}∼N1/4) unitary steps of Grover's algorithm suffices to perfectly prepare a Dicke state of NNN atoms in a cavity. We also show that a few subsequent Grover steps can be employed to generate GHZ and Cat states. The Grover iteration is physically realized by global qubit rotations and by the phase shift of single photons reflected on the cavity. Our protocols are deterministic and require no individual addressing of the atoms. A detailed error analysis accounting for spatial mode matching of the photon to the cavity, spontaneous emission, mirror scattering, and the finite bandwidth of the photon mode is used to predict the fidelity of the prepared states as a function of system parameters and atom-cavity cooperativity. The fidelity can be increased by heralding on detection of the reflected photon.