Flux qubit on a mesoscopic nonsuperconducting ring

Zipper, E.; Kurpas, Marcin; Szeląg, M; Dajka, Jerzy; Szopa, M.

doi:10.1103/physrevb.74.125426

Cited by 41 publications

(42 citation statements)

References 32 publications

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“…Quantum tunneling should thus lead to a qubit i.e. a quantum superposition of the two opposed current states [9,10].…”

Section: Qubitsmentioning

confidence: 99%

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Persistent currents in distorted quantum ring

Szeląg

Szopa²

2008

J. Phys.: Conf. Ser.

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Abstract. Persistent currents in distorted narrow mesoscopic rings threaded by the magnetic flux of the Aharonow Bohm type are investigated. It is shown that the ring distortions can be modelled by an appropriate potential term. The cases with a single and multiple distortions are considered. The single distortion opens a gap in the electron energy spectrum of a ring and decreases the amplitude of persistent currents. It is shown that in the ring with multiple distortions, under some geometrical conditions, there is an enhancement of the persistent current and some of the electronic states remain degenerated. The possible application of the model to the formation of a qubit is discussed. IntroductionDuring the last 20 years, persistent currents (PC) in mesoscopic rings have attracted significant interest both theoretically and experimentally [1][2][3][4]. PC in small quantum rings threaded by a magnetic flux are a manifestation of quantum coherence in a submicron system. If the ring circumference L is smaller than the phase coherence L φ the electron wave function may extend coherently over L even in the presence of elastic scatterers. In other words a normal loop with L < L φ has a nontrivial ground state with a circulating PC.In this paper we present theoretical study of persistent currents in the quantum ring. We consider a narrow ring with two distortions of uniform cross section lying on a plane (Fig. 1). We show that quantum tunneling between states with nearly equal energy and PC can lead to a formation of a qubit. The paper is organized as follows. In Sec. 2, we write down and disscus the Schrödinger equation for one electron in the ring with two distoritons in the presence of a magnetic flux. We show that the curvature of distorted ring enters into the Schrödinger equation via a geometrical potential term [5]. We demonstrate that the factorization of the wave function leads to two separate eigenequations in transverse and longitudinal directions. In Sec. 3 we analyze a distorted quantum ring consisting of eight constant-curvature segments and we find the energy spectrum of such a ring. We show that the geometrical potential V g opens gaps in the electron energy spectrum with the exception of the case when distortions are symmetrically placed. Next, in section 4 we perform analitycal calculations and computer simulations to analyze the effect of distortions on the persistent currents. We show that in the case of a small one-dimensional ring the presence of distortions significantly changes the currents and especially how the currents are affected by various configuration of distortions. In Sec. 5 we show that distorted quantum ring can be useful for quantum computing hardware. Conclusions are presented in Sec. 6.

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“…Quantum tunneling should thus lead to a qubit i.e. a quantum superposition of the two opposed current states [9,10].…”

Section: Qubitsmentioning

confidence: 99%

“…If we assume e.g. that N = N odd and Φ Φ 0 close to 1 2 these states are |n F +1 = |µ and |−n F = |ν [9] and the Hamiltonian (19) becomes…”

Section: Qubitsmentioning

confidence: 99%

Persistent currents in distorted quantum ring

Szeląg

Szopa²

2008

J. Phys.: Conf. Ser.

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“…50 Since a persistent current due to excitons can be initiated and controlled optically, 22 it can be speculated that an exciton qubit in a nanoring can be formed whose function rests upon the exciton Aharonov-Bohm effect.…”

Section: Discussionmentioning

confidence: 99%

Noncircular semiconductor nanorings of types I and II: Emission kinetics in the excitonic Aharonov-Bohm effect

Grochol

Zimmermann

2007

Phys. Rev. B

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Transition energies and oscillator strengths of excitons in dependence on magnetic field are investigated in type I and II semiconductor nanorings. A slight deviation from circular (concentric) shape of the type II nanoring gives a better observability of the Aharonov-Bohm oscillations since the ground state is always optically active. Kinetic equations for the exciton occupation are solved with acoustic phonon scattering as the major relaxation process, and absorption and luminescence spectra are calculated showing deviations from equilibrium. The presence of a non-radiative exciton decay leads to a quenching of the integrated photoluminescence with magnetic field.

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“…The amplitude of this oscillatory component corresponds to a persistent current. Recently, a sudden application of persistent currents in the quantum computing was proposed by Zipper et al [23]. They argue that semiconductor or metal rings with a barrier can lead to a formation of a qubit at low temperatures.…”

Section: Introductionmentioning

confidence: 99%