arXiv:quant-ph/0203145 · Physical review. B, Condensed matter

Quantum computation with coupled quantum dots embedded in optical microcavities

Xin-Qi Li, YiJing Yan

Published Apr 23, 2002• 31 citations

Abstract

Based on an idea that spatial separation of charge states can enhance quantum coherence, we propose a scheme for a quantum computation with the quantum bit (qubit) constructed from two coupled quantum dots. Quantum information is stored in the electron-hole pair state with the electron and hole located in different dots, which enables the qubit state to be very long-lived. Universal quantum gates involving any pair of qubits are realized by coupling the quantum dots through the cavity photon which is a hopeful candidate for the transfer of long-range information. The operation analysis is carried out by estimating the gate time versus the decoherence time.

DOI: 10.1103/physrevb.65.205301

Related papers

Highly coherent solid-state quantum bit from a pair of quantum dots

Xin-Qi Li, YiJing Yan

In this letter, we propose a scheme to buildup a highly coherent solid-state quantum bit (qubit) from two coupled quantum dots. Quantum information is stored in the state of the electron-hole pair with the electron and hole located in different dots, and universal quantum gates involving any pair of qubits are realized by effective coupling interaction via virtually exchanging cavity photons.

arXiv:quant-ph/0204027Applied Physics LettersJul 1, 20025 citations

Quantum computation with quantum dots and terahertz cavity quantum electrodynamics

Mark S. Sherwin, Ataç İmamoğlu, T. E. Montroy

A quantum computer is proposed in which information is stored in the two lowest electronic states of doped quantum dots (QD's). Many QD's are located in a microcavity. A pair of gates controls the energy levels in each QD. A controlled-NOT (C-NOT) operation involving any pair of QD's can be effected by a sequence of gate-voltage pulses which tune the QD energy levels into resonance with frequencies of the cavity or a laser. The duration of a C-NOT operation is estimated to be much shorter than the time for an electron to decohere by emitting an acoustic phonon.

arXiv:quant-ph/9903065Physical Review ANov 1, 1999143 citations

Single qubit from two coupled quantum dots: An approach to semiconductor quantum computations

Xin-Qi Li, Yasuhiko Arakawa

A scheme to possibly implement the quantum computer is proposed based on the idea to build up the single qubit from two coupled quantum dots. The spatial separation of the two logic states of the qubit can greatly reduce the decoherence time, which allows one to perform the coherent quantum logic operations at a fairly high ratio. Together with the realization of the universal quantum logic gates, and the proper scheme of quantum measurement, the present proposal can satisfy all the essential criteria for quantum computing.

Physical Review ADec 7, 200044 citations

Ultrafast optical control of individual quantum dot spin qubits

Kristiaan De Greve, David Press, Peter L. McMahon +1 more

Single spins in semiconductor quantum dots form a promising platform for solid-state quantum information processing. The spin-up and spin-down states of a single electron or hole, trapped inside a quantum dot, can represent a single qubit with a reasonably long decoherence time. The spin qubit can be optically coupled to excited (charged exciton) states that are also trapped in the quantum dot, which provides a mechanism to quickly initialize, manipulate and measure the spin state with optical pulses, and to interface between a stationary matter qubit and a 'flying' photonic qubit for quantum communication and distributed quantum information processing. The interaction of the spin qubit with light may be enhanced by placing the quantum dot inside a monolithic microcavity. An entire system, consisting of a two-dimensional array of quantum dots and a planar microcavity, may plausibly be constructed by modern semiconductor nano-fabrication technology and could offer a path toward chip-sized scalable quantum repeaters and quantum computers. This article reviews the recent experimental developments in optical control of single quantum dot spins for quantum information processing. We highlight demonstrations of a complete set of all-optical single-qubit operations on a single quantum dot spin: initialization, an arbitrary SU(2) gate, and measurement. We review the decoherence and dephasing mechanisms due to hyperfine interaction with the nuclear-spin bath, and show how the single-qubit operations can be combined to perform spin echo sequences that extend the qubit decoherence from a few nanoseconds to several microseconds, more than 5 orders of magnitude longer than the single-qubit gate time. Two-qubit coupling is discussed, both within a single chip by means of exchange coupling of nearby spins and optically induced geometric phases, as well as over longer-distances. Long-distance spin-spin entanglement can be generated if each spin can emit a photon that is entangled with the spin, and these photons are then interfered. We review recent work demonstrating entanglement between a stationary spin qubit and a flying photonic qubit. These experiments utilize the polarization- and frequency-dependent spontaneous emission from the lowest charged exciton state to single spin Zeeman sublevels.

Reports on Progress in PhysicsSep 1, 201369 citations

Quantum Information Processing Using Quantum Dot Spins and Cavity QED

Ataç İmamoğlu, D. D. Awschalom, Guido Burkard +4 more

The electronic spin degrees of freedom in semiconductors typically have decoherence times that are several orders of magnitude longer than other relevant time scales. A solid-state quantum computer based on localized electron spins as qubits is therefore of potential interest. Here, a scheme that realizes controlled interactions between two distant quantum dot spins is proposed. The effective long-range interaction is mediated by the vacuum field of a high finesse microcavity. By using conduction-band-hole Raman transitions induced by classical laser fields and the cavity-mode, parallel controlled-not operations, and arbitrary single qubit rotations can be realized.

arXiv:quant-ph/9904096Physical Review LettersNov 15, 19991,993 citations

Quantum Computation Using Optically Coupled Quantum Dot Arrays

Prabhakar Pradhan, M. P. Anantram, K. L. Wang +2 more

A solid state model for quantum computation has potential advantages in terms of the ease of fabrication, characterization, and integration. The fundamental requirements for a quantum computer involve the realization of basic processing units (qubits), and a scheme for controlled switching and coupling among the qubits, which enables one to perform controlled operations on qubits. We propose a model for quantum computation based on optically coupled quantum dot arrays, which is computationally similar to the atomic model proposed by Cirac and Zoller. In this model, individual qubits are comprised of two coupled quantum dots, and an array of these basic units is placed in an optical cavity. Switching among the states of the individual units is done by controlled laser pulses via near field interaction using the NSOM technology. Controlled rotations involving two or more qubits are performed via common cavity mode photon. We have calculated critical times, including the spontaneous emission and switching times, and show that they are comparable to the best times projected for other proposed models of quantum computation. We have also shown the feasibility of accessing individual quantum dots using the NSOM technology by calculating the photon density at the tip, and estimating the power necessary to perform the basic controlled operations. We are currently in the process of estimating the decoherence times for this system; however, we have formulated initial arguments which seem to indicate that the decoherence times will be comparable, if not longer, than many other proposed models.

Jan 1, 19980 citations