We present an adiabatic approach to the design of entangling quantum operations with two electron spins localized in separate InAs/GaAs quantum dots via the Coulomb interaction between optically excited localized states. Slowly varying optical pulses minimize the pulse noise and the relaxation of the excited states. An analytical ``dressed-state'' solution gives a clear physical picture of the entangling process and a numerical solution is used to investigate the error dynamics. For two vertically stacked quantum dots we show that, for a broad range of dot parameters, a two-spin state with concurrence $C>0.85$ can be obtained by four optical pulses with durations $\ensuremath{\sim}0.1--1\text{ }\text{ns}$.We present an adiabatic approach to the design of entangling quantum operations with two electron spins localized in separate InAs/GaAs quantum dots via the Coulomb interaction between optically excited localized states. Slowly varying optical pulses minimize the pulse noise and the relaxation of the excited states. An analytical ``dressed-state'' solution gives a clear physical picture of the entangling process and a numerical solution is used to investigate the error dynamics. For two vertically stacked quantum dots we show that, for a broad range of dot parameters, a two-spin state with concurrence $C>0.85$ can be obtained by four optical pulses with durations $\ensuremath{\sim}0.1--1\text{ }\text{ns}$.

arXiv:0802.1527Physical Review BDec 22, 200813 citations

Optical locking of a quantum dot electron spin qubit

Jonathan H. Bodey, Claire Le Gall, Robert Stockill +3 more

Bulletin of the American Physical SocietyMar 6, 20190 citations

High-fidelity optical quantum gates based on type-II double quantum dots in a nanowire

Masoomeh Taherkhani, Morten Willatzen, Emil V. Denning +2 more

We propose an optical gating scheme for quantum computing based on crystal-phase type II double quantum dots in an InP nanowire. The qubit is encoded on the electron spin and the gate operations are performed using stimulated Raman adiabatic passage (STIRAP), using the orbital degree of freedom in double quantum dots to form an auxiliary ground state. Successful STIRAP gating processes require an efficient coupling of both qubit ground states of the double quantum dot to the gating auxiliary ground state, and we demonstrate that this can be achieved using a charged exciton state. Crucially, by using type II dots, the hole is localized between the two spatially separated electrons in the charged exciton complex, thereby efficiently coupling the electron ground-state orbitals. By taking advantage of the high-fidelity state transfer by means of STIRAP in type II double quantum dots, we propose a protocol for coherently manipulating the spin-orbital quantum state of confined electrons in a quantum dot chain of an InP nanowire. We subsequently exploit the protocol to realize single- and two-qubit gates with fidelity above 0.99.We propose an optical gating scheme for quantum computing based on crystal-phase type II double quantum dots in an InP nanowire. The qubit is encoded on the electron spin and the gate operations are performed using stimulated Raman adiabatic passage (STIRAP), using the orbital degree of freedom in double quantum dots to form an auxiliary ground state. Successful STIRAP gating processes require an efficient coupling of both qubit ground states of the double quantum dot to the gating auxiliary ground state, and we demonstrate that this can be achieved using a charged exciton state. Crucially, by using type II dots, the hole is localized between the two spatially separated electrons in the charged exciton complex, thereby efficiently coupling the electron ground-state orbitals. By taking advantage of the high-fidelity state transfer by means of STIRAP in type II double quantum dots, we propose a protocol for coherently manipulating the spin-orbital quantum state of confined electrons in a quantum dot chain of an InP nanowire. We subsequently exploit the protocol to realize single- and two-qubit gates with fidelity above 0.99.

Physical review. B./Physical review. BApr 10, 201911 citations

Modelling of Optical Gates for Quantum Information Processing.

Masoomeh Taherkhani

A numerical tool is developed to calculate the exciton energy and oscillator strength in newly emerged type-II nanowire quantum-dots. For a singlequantum-dot, the poor overlap of the electron part and the weakly conﬁned hole part of the exciton wavefunction leads to a small oscillator strength compared to type-I systems. To increase the oscillator strength, we propose a double-quantum-dot structure featuring a strongly localized exciton wavefunction and a corresponding four-fold relative enhancement of the oscillator strength, paving the way towards eﬃcient optically controlled quantum gate applications in the type-II nanowire system. Next, an optical gating scheme for quantum computing based on type-II double-quantum-dots is proposed. The qubit is encoded on the electron spin and the gate operations are performed by stimulated Raman adiabatic passage (STIRAP) using the position degree of freedom in double-quantum-dots to form an auxiliary ground-state. Successful STIRAP gating processes require an eﬃcient coupling of both qubit ground-states of the double-quantum-dot to the gating auxiliary state and we demonstrate that this can be achieved using a charged exciton state. Crucially, by using type-II quantum-dots, the hole is localized between the two spatially separated electrons in the chargedexciton complex, thereby eﬃciently coupling the electron states orbitals. We subsequently exploit the scheme to realize single- and two-qubit gates for quantum computation. The conditional operation is performed by using Coulomb coupling to induce a shift of the STIRAP transition frequencies leading to a conditional violation of the STIRAP two-photon resonance. We calculate the ﬁdelity of gates and show their performance is robust against the spin and charge noises.A numerical tool is developed to calculate the exciton energy and oscillator strength in newly emerged type-II nanowire quantum-dots. For a singlequantum-dot, the poor overlap of the electron part and the weakly conﬁned hole part of the exciton wavefunction leads to a small oscillator strength compared to type-I systems. To increase the oscillator strength, we propose a double-quantum-dot structure featuring a strongly localized exciton wavefunction and a corresponding four-fold relative enhancement of the oscillator strength, paving the way towards eﬃcient optically controlled quantum gate applications in the type-II nanowire system. Next, an optical gating scheme for quantum computing based on type-II double-quantum-dots is proposed. The qubit is encoded on the electron spin and the gate operations are performed by stimulated Raman adiabatic passage (STIRAP) using the position degree of freedom in double-quantum-dots to form an auxiliary ground-state. Successful STIRAP gating processes require an eﬃcient coupling of both qubit ground-states of the double-quantum-dot to the gating auxiliary state and we demonstrate that this can be achieved using a charged exciton state. Crucially, by using type-II quantum-dots, the hole is localized between the two spatially separated electrons in the chargedexciton complex, thereby eﬃciently coupling the electron states orbitals. We subsequently exploit the scheme to realize single- and two-qubit gates for quantum computation. The conditional operation is performed by using Coulomb coupling to induce a shift of the STIRAP transition frequencies leading to a conditional violation of the STIRAP two-photon resonance. We calculate the ﬁdelity of gates and show their performance is robust against the spin and charge noises.

Jan 1, 20180 citations

Optical control of one and two hole spins in interacting quantum dots

A. Greilich, Sam Carter, Daniel C. Kim +2 more

arXiv:1107.0211Nature PhotonicsSep 23, 2011159 citations

C>0.85

can be obtained by four optical pulses with durations $\ensuremath{\sim}0.1--1\text{ }\text{ns}$.