Selective coherent destruction of tunneling in a quantum-dot array

Abstract

The coherent manipulation of quantum states is one of the main tasks required in quantum computation. In this paper we demonstrate that it is possible to control coherently the electronic position of a particle in a quantum-dot array. By tuning an external ac electric field we can selectively suppress the tunneling between dots, trapping the particle in a determined region of the array. The problem is treated non-perturbatively by a time-dependent Hamiltonian in the effective mass approximation and using Floquet theory. We find that the quasienergy spectrum exhibits crossings at certain field intensities that result in the selective suppression of tunneling. The search for a solid-state based quantum computer device has attracted a lot of interest in the physics community recently. The ability to manipulate a quantum state and measure it is one of the most important and pressing challenges to be addressed in real implementations. Fortunately great advances in this area have been achieved recently. A good example of that are the Rabi oscillations observed in exciton states of self-assembled quantum dots (QDs). 1,2,3,4Our work here is based on the coherent destruction of tunneling (CDT) of a driven two-level system, 5,6,7 in which the tunneling of one particle in a symmetric double well potential is suppressed for some special value of frequency and field intensity. We propose a system in which one can selectively suppress the tunneling between individual quantum dots tuned by the external ac electric field. This effect provides one with a different experimental handle to control a quantum mechanical system. By suitable variation of the frequency and applied ac field amplitude, one can precise the location of one electron in the multidot array. To demonstrate this effect, our model employs an effective mass nearest-neighbor tight-biding approximation (NNTB).8,9,10 The dynamics is analyzed using Floquet theory and the direct integration of the time-dependent Schrödinger equation.The Hamiltonian for an electron in an array of identical QDs under a strong ac field within NNTB is written as(1) where T e is the hopping matrix element, a † j and a j are, respectively, the electron creation and annihilation operator in the dot j, e is the electronic charge, F is the field intensity, d is the separation between dots, ω is the field frequency, and φ is the phase of the drive field. This phase, first thought to be a non-relevant factor, is in fact quite an important parameter in the CDT at smaller frequency, as we have recently shown.11 Indeed, a phase φ = π/2 produces a much better dynamic localization than any other possible phase φ, and consequently it is our choice here.Since H is periodic in time (H(t) = H(t + τ ), where τ = 2π/ω is the period) we can make use of the standard Floquet theory 7,12 and write the solutions of the time-dependent Schrödinger equation as ψ(t) = exp(−iεt/h)u(t), where u(t), the so-called Floquet state, is also periodic in time with the same period τ , and ε is the Floquet characteristic expone...

Dynamic localization in Glauber–Fock lattices

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Producing directed migration with correlated atoms in a tilted ac-driven lattice

“…The celebrated Bloch oscillations (BO) is one of the direct quantum controls of a wavepacket moving in a tilted lattice [16]. On the other hand, a periodically driving field can lead to photon-assisted tunneling [17], dynamical localization (DL) [18,19], and coherent destruction of tunneling (CDT) [20][21][22][23], etc [24][25][26]. These effects provide potential application for quantum control, and give better understanding of the solid state physics.…”

Coherent destruction of tunneling in a lattice array under selective in-phase modulations

“…The coherent destruction of tunneling (CDT) [3] and dynamical localization (DL) [4] are two seminal results in this field. Moreover, some important generalizations of CDT, such as selective coherent destruction of tunneling (SCDT) [5], non-degenerate CDT [6], nonlinear CDT [7], and manybody CDT [8], have also been explored. Single-particle CDT and DL [9,10], which have been observed experimentally in optical traps, attract considerable attention due to their potential applications in quantum motor [11,12] and quantum information processing [13].…”