Single-qubit operations in the double-donor structure driven by optical and voltage pulses

Abstract

We study theoretically the quantum dynamics of an electron in the singlyionized double-donor structure in the semiconductor host under the influence of laser pulses whose frequencies are close to structure resonant frequencies. This system can be used as a charge qubit where the logical states are defined by the lowest two energy states of the remaining valence electron localized around one or another donor. The quantum operations are performed via resonant or Raman-like transitions between the localized (qubit) states and the excited states delocalized over the structure, combined with phase shifts between qubit states generated by voltage pulses. The possibility of realization of arbitrary single-qubit rotations is demonstrated.

Coupled donors in quantum dots: Quantum size and dielectric mismatch effects

“…17,18 In such schemes, the decoherence caused by the ionization and spontaneous emission of the excited states acting as connecting channels between the logical states could be minimized through the proper choice of QD size and dielectric environment. On one hand, quantum confinement would lift the quasidegeneracy among near-continuum states, increasing the corresponding ionization threshold and excitation selectivity.…”

“…This system encodes the logical information either on the spin or on the charge degrees of freedom of the remaining excess electron. [14][15][16][17][18][19][20] Initial proposals relied on spin encoding. However, direct detection of a single spin remains today a major challenge.…”

Laser-induced operations with charge qubits in a double-well nanostructure

“…In particular, much attention is now paid to the charge qubits based on the tunnel-coupled quantum dots [5][6][7]13,15] or a singly ionized pair of donor atoms nearby the surface [8,[16][17][18], the basis qubit states |0 and |1 being the orbital electron states |L and |R localized in different (left and right) quantum dots or at different donor sites. Operations with such qubits can be implemented, first, through the changes in the energies E L , E R of the states |L , |R and the height of the barrier separating the minima of the double-well potential (by the adiabatic changes in the voltages at corresponding gates [5][6][7][8]) and, second, through the influence of the resonant (tuned to the resonance with one of the excited levels that plays a role of the "transport" level) or nonresonant laser pulse [13,[18][19][20][21][22][23][24][25][26]. τ on the time t op of single-qubit operations [16][17][18][27][28][29][30].…”

“…The energy spectrum of a singly ionized pair of donor atoms in silicon is even more complex because of both the strong degeneracy of excited states of each donor considered as a hydrogen-like atom and the six-fold degeneracy of the silicon conduction band. In the case of nonresonant pulses, the proximity of excited levels to each other is not detrimental, but the value of t op greatly increases [21,23,24,26].…”

“…As will be shown below, the problem of laserinduced transitions |0 → |1 , |1 → |0 in such a four-level system allows for an exact solution within the standard rotating wave approximation (RWA), without additional approximations like the adiabatic elimination of high-lying levels [32]. Relatively simple analytical expressions for the dependencies of the state amplitudes on time not only help to analyze the results of numerical calculations on much more complex systems [24,31] but enable to find out a novel regime of laser-iduced operations with charge qubits that differs from both resonant and nonresonant (in a commonly accepted interpretation [23,24,26]) regimes.…”