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Physical Review B

Optically pumping hole spins in coupled quantum dot molecules into a steady state of high concurrence entanglement

Song Yang, Ming Gong, ChuanFeng Li, Xu‐Bo Zou, Guang‐Can Guo

Published Dec 16, 2009• 3 citations
Publisher

Abstract

We present a way to prepare a high concurrence steady state entanglement of two hole spins in a quantum dot molecule. We show that the spontaneous dissipation can be used to induce and stabilize the entanglement with rapid rate. By optical pumping of trion levels, two-qubit singlet state can be automatically generated. We also show that our proposal can synchronously accomplish both initialization and entanglement generation. The effects of acoustic phonons and electron tunneling are also discussed and we find that the main influence is from deformation potential coupling to acoustic phonons in InAs/GaAs quantum dots. At low temperature, we show that concurrence of entanglement can be greater than 0.95 at $T=1\text{ }\text{K}$.

DOI
10.1103/physrevb.80.235322

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We present a way to prepare a high concurrence steady state entanglement of two hole spins in a quantum dot molecule. We show that the spontaneous dissipation can be used to induce and stabilize the entanglement with rapid rate. By optical pumping of trion levels, two-qubit singlet state can be automatically generated. We also show that our proposal can synchronously accomplish both initialization and entanglement generation. The effects of acoustic phonons and electron tunneling are also discussed and we find that the main influence is from deformation potential coupling to acoustic phonons in InAs/GaAs quantum dots. At low temperature, we show that concurrence of entanglement can be greater than 0.95 at T=1 KT=1\text{ }\text{K}T=1 K.
Entanglement, a non-trivial phenomena manifested in composite quantum system, can be served as a new type of physical resource in the emerging technology of quantum information and quantum computation. However, a quantum entanglement is fragile to the environmental-induced decoherence. Here, we present a novel way to prepare a high-concurrence steady-state entanglement of two hole spins in a quantum dot molecular via optical pumping of trion levels. In this scheme, the spontaneous dispassion is used to induce and stabilize the entanglement with rapid rate. It is firstly shown that under certain conditions, two-qubit singlet state can be generated without requiring the state initialization. Then we study the effect of acoustic phonons and electron tunnelings on the scheme, and show that the concurrence of entangled state can be over 0.95 at temperature $T = 1 $K.
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The spin states of electrons and holes confined in InAs quantum dot molecules have recently come to fore as a promising system for the storage or manipulation of quantum information. We describe here a feasible scheme for complete quantum optical control of two electron spin qubits in two vertically-stacked singly-charged InAs quantum dots coupled by coherent electron tunneling. With an applied magnetic field transverse to the growth direction, we construct a universal set of gates that corresponds to the possible Raman transitions between the spin states. We detail the procedure to decompose a given two-qubit unitary operation, so as to realize it with a successive application of up to 8 of these gates. We give the pulse shapes for the laser pulses used to implement this universal set of gates and demonstrate the realization of the two-qubit quantum Fourier transform with fidelity of 0.881 and duration of 414 ps. Our proposal therefore offers an accessible path to universal computation in quantum dot molecules and points to the advantages of using pulse shaping incoherent manipulation of optically active quantum dots to mitigate the negative effects of unintended dynamics and spontaneous emission.
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Tunnel-coupled optically active quantum dot molecules (QDMs) have the potential to operate as spin-photon interfaces with coupled spins that interact with two different photon frequencies at the same time. A prerequisite is to deterministically prepare two (electron or hole) spins in the QDM and be able to electrically tune the orbital state couplings. Here, we demonstrate the sequential optical charging of a single QDM with two-electron spins while simultaneously maintaining the ability to widely tune orbital couplings using static electric fields and optically drive the system for quantum light generation. We optically prepare one- and two-spin states, initialize via optical pumping and explore orbital and spin relaxation dynamics for one- and two-spin states as a function of the energy detuning and hybridization of orbital states. For two-spin states, remarkably long singlet-triplet relaxation times are observed, extending beyond ∼ 100 μ s with strong dependence on the relative energy of ground and excited two-spin states. Qualitative agreement is observed with k · p calculations of phonon-mediated spin relaxation. Our results provide new quantitative understanding of the dynamics of one- and two-spin states and address a number of key prerequisites for using QDMs to create multidimensional photonic cluster states.