A simple quantum gate with atom chips (original) (raw)
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Theoretical analysis of a realistic atom-chip quantum gate
Physical Review A, 2006
We present a detailed, realistic analysis of the implementation of a proposal for a quantum phase gate based on atomic vibrational states, specializing it to neutral rubidium atoms on atom chips. We show how to create a double-well potential with static currents on the atom chips, using for all relevant parameters values that are achieved with present technology. The potential barrier between the two wells can be modified by varying the currents in order to realize a quantum phase gate for qubit states encoded in the atomic external degree of freedom. The gate performance is analyzed through numerical simulations; the operation time is ∼ 10 ms with a performance fidelity above 99.9%. For storage of the state between the operations the qubit state can be transferred efficiently via Raman transitions to two hyperfine states, where its decoherence is strongly inhibited. In addition we discuss the limits imposed by the proximity of the surface to the gate fidelity.
Journal of the Physical Society of Japan, 2011
We propose a scalable neutral atom quantum computer with an on-demand interaction through a selective two-qubit gate operation. Atoms are trapped by a lattice of near field Fresnel diffraction lights so that each trap captures a single atom. One-qubit gate operation is implemented by a gate control laser beam which is applied to an individual atom. Two-qubit gate operation between an arbitrary pair of atoms is implemented by sending these atoms to a state-dependent optical lattice and making them collide so that a particular two-qubit state acquires a dynamical phase. We give numerical evaluations corresponding to these processes, from which we estimate the upper bound of a two-qubit gate operation time and corresponding gate fidelity. Our proposal is feasible within currently available technology developed in cold atom gas, MEMS, nanolithography, and various areas in optics.
Operation of a quantum phase gate using neutral atoms in microscopic dipole traps
Physical Review A, 2002
In this paper we propose and analyze various operating regimes of a quantum phase gate built on two atoms trapped in two independent dipole traps. The gate operates when the atoms are excited using a two-photon transition from the hyperfine manifold of ground states up to Rydberg states with strong dipole-dipole interaction. Experimental requirements are discussed to reach a fast ͑microsecond͒ gate operation.
Selective Application of Two-Qubit Gate in Neutral Atom Quantum Computer
2011
We propose a scalable neutral atom quantum computer with an on-demand interaction through a selective two-qubit gate operation. Atoms are trapped by a lattice of near field Fresnel diffraction lights so that each trap captures a single atom. One-qubit gate operation is implemented by a gate control laser beam which is applied to an individual atom. Two-qubit gate operation between an arbitrary pair of atoms is implemented by sending these atoms to a state-dependent optical lattice and making them collide so that a particular two-qubit state acquires a dynamical phase. We give numerical evaluations corresponding to these processes, from which we estimate the upper bound of a two-qubit gate operation time and corresponding gate fidelity. Our proposal is feasible within currently available technology developed in cold atom gas, MEMS, nanolithography, and various areas in optics.
Microwave potentials and optimal control for robust quantum gates on an atom chip
Physical Review A, 2006
We propose a two-qubit collisional phase gate that can be implemented with available atom chip technology, and present a detailed theoretical analysis of its performance. The gate is based on earlier phase gate schemes, but uses a qubit state pair with an experimentally demonstrated, very long coherence lifetime. Microwave near-fields play a key role in our implementation as a means to realize the state-dependent potentials required for conditional dynamics. Quantum control algorithms are used to optimize gate performance. We employ circuit configurations that can be built with current fabrication processes, and extensively discuss the impact of technical noise and imperfections that characterize an actual atom chip. We find an overall infidelity compatible with requirements for fault-tolerant quantum computation.
A Nanophotonic Quantum Phase Switch with a Single Atom
Frontiers in Optics 2014, 2014
In analogy to transistors in classical electronic circuits, a quantum optical switch is an important element of quantum circuits and quantum networks [1][2]. Operated at the fundamental limit where a single quantum of light or matter controls another field or material system[4], it may enable fascinating applications such as long-distance quantum communication , distributed quantum information processing[2] and metrology , and the exploration of novel quantum states of matter . Here, by strongly coupling a photon to a single atom trapped in the near field of a nanoscale photonic crystal cavity, we realize a system where a single atom switches the phase of a photon, and a single photon modifies the atom's phase. We experimentally demonstrate an atom-induced optical phase shift[8] that is nonlinear at the two-photon level[9], a photon number router that separates individual photons and photon pairs into different output modes[10], and a single-photon switch where a single "gate" photon controls the propagation of a subsequent probe field 12]. These techniques pave the way towards integrated quantum nanophotonic networks involving multiple atomic nodes connected by guided light.
MIXED INTERNAL-EXTERNAL STATE APPROACH FOR QUANTUM COMPUTATION WITH NEUTRAL ATOMS ON ATOM CHIPS
Current Topics in Atomic, Molecular and Optical Physics - Invited Lectures of TC-2005, 2007
We present a realistic proposal for the storage and processing of quantum information with cold 87 Rb atoms on atom chips. The qubit states are stored in hyperfine atomic levels with long coherence time, and two-qubit quantum phase gates are realized using the motional states of the atoms. Two-photon Raman transitions are used to transfer the qubit information from the internal to the external degree of freedom. The quantum phase gate is realized in a double-well potential created by slowly varying dc currents in the atom chip wires. Using realistic values for all experimental parameters (currents, magnetic fields, ...) we obtain high gate fidelities (above 99.9%) in short operation times (~ 10 ms).
Quantum gates with neutral atoms: Controlling collisional interactions in time-dependent traps
Physical Review A, 2000
We theoretically study specific schemes for performing a fundamental two-qubit quantum gate via controlled atomic collisions by switching microscopic potentials. In particular we calculate the fidelity of a gate operation for a configuration where a potential barrier between two atoms is instantaneously removed and restored after a certain time. Possible implementations could be based on microtraps created by magnetic and electric fields, or potentials induced by laser light.
Geometric Unitary Gates in Cold Atom Ensembles on an Atom Chip
We propose a feasible scheme to achieve quantum computation based on geometric manipulation of ensembles of atoms and analyze it for neutral rubidium atoms magnetically trapped in planoconcave microcavities on an atom chip. The geometric operations are accomplished by optical excitation of a single atom into a Rydberg state in a constant electric field. Strong dipole-dipole interactions and incident lasers drive the dark state of the atom ensembles to undergo cyclic evolutions that realize a universal set of quantum gates. Such geometric manipulation turns out naturally to protect the qubits from the errors induced by nonuniform laser illumination as well as cavity loss. The gate performance and decoherence processes are assessed by numerical simulation.