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The Journal of Physical Chemistry C

Quantum Computing with Exciton Qubits in Colloidal Semiconductor Nanocrystals

Dulanjan Harankahage, James Cassidy, Mingrui Yang, Dmitry Porotnikov, Maia Williams, Natalia Kholmicheva, Mikhail A. Zamkov

Published Oct 4, 2021• 24 citations
Publisher

Abstract

The present work evaluates the feasibility of quantum computing with exciton qubits in coupled colloidal semiconductor nanocrystals (NCs). A strategy for manipulating two-qubit states of colloidal NC hetero-dimers is described. We show that a sequence of laser pulses with the same photon energy can bring excitonic states of a nanocrystal hetero-dimer into entanglement and perform arbitrary qubit rotations (quantum gates). Our simulations of a realistic two-particle assembly of CdSe/CdS core/shell NCs demonstrate that such two-qubit gate operations can be driven by optical parametric oscillators with a theoretical error of 0.1%. A strategy for upscaling two-qubit hetero-dimers to N -qubit exciton gates in semiconductor NC assemblies is discussed.

DOI
10.1021/acs.jpcc.1c05009

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The present work evaluates the feasibility of quantum computing with exciton qubits in coupled colloidal semiconductor nanocrystals (NCs). A strategy for manipulating two-qubit states of colloidal NC hetero-dimers is described. We show that a sequence of laser pulses with the same photon energy can bring excitonic states of a nanocrystal hetero-dimer into entanglement and perform arbitrary qubit rotations (quantum gates). Our simulations of a realistic two-particle assembly of CdSe/CdS core/shell NCs demonstrate that such two-qubit gate operations can be driven by optical parametric oscillators with a theoretical error of 0.1%. A strategy for upscaling two-qubit hetero-dimers to N -qubit exciton gates in semiconductor NC assemblies is discussed.
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The optically active nature of direct bandgap semiconductors makes them well suited for applications in quantum optics. Semiconductor quantum dots (QDs) are particularly promising, due to their discrete atom-like energy levels. In this thesis, transitions between these energy levels are used to investigate the effects of electric and magnetic fields on the energy structure of single QDs, with a view to developing applications in the field of quantum computing. In the work presented here a novel method of creating entangled photon pair emitters is presented, in which an electric field is used to tune the energy structure of single QDs to allow the fidelity of the emitted entangled state to be increased. In addition, a technique for the creation of energy-tunable entangled photon pairs is proposed and shown to be feasible with current technology. Furthermore, the potential of QDs to act as an interface between photonic and spin qubits is explored. Application of a time varying electric field is used to dynamically tune the QD energy levels, allowing the evolution of excitons confined within single QDs to be manipulated. Using this system a controlled phase rotation of the exciton spin state is implemented. Finally, indistinguishable single photons, emitted by the radiative decay of the exciton state, are used to generate the input state for an integrated photonic two-qubit quantum logic gate. This is the first demonstration of a two-qubit gate using on-demand single photons. It is also the first demonstration of such a gate with all components realised using semiconductor materials.
A review of semiconductor-based schemes for the implementation of quantum information processing devices is presented. After recalling the fundamentals of quantum information/computation theory, we shall discuss two potential implementation schemes based on charge degrees of freedom in semiconductor nanostructures. More specifically, we shall present an all-optical implementation of quantum information processing with semiconductor macroatoms/molecules. In this case the computational degrees of freedom are interband optical transitions driven by ultrafast sequences of multicolor laser-pulse trains. As alternative approach, we shall also discuss a transport-like scheme based on ballistic electrons in coupled semiconductor quantum wires. Within such implementation strategy, we shall finally propose a relatively simple quantum gating sequence for testing Bell inequality violations in a condensed-matter environment.
Potential application of elementary excitation in semiconductor quantum dot to quantum computation is discussed. Construction of scalable hardware and all optical implementation of logical gate that exploits discrete nature of electron-hole states and their well concentrated oscillator strenth for ultrafast gate operation are proposed. Rabi population oscillation of an excitonic two-level system in an isolated single InxGa1-xAs quantum dot is manifested by a quantum wave function interferometry in time domain, demonstrating a long lived coherence of zero-dimensional excitonic states and revealed the coherent population flopping under strong optical field. A phase-sensitive coherent gate operation on single-dot exciton qubit is demonstrated.
This paper discusses the potential application of elementary excitation in semiconductor quantum dots to quantum computation. We propose a scalable hardware design and all-optical implementation of logical gates that exploit the discrete nature of electron and hole states and their well-concentrated oscillator strength for ultrafast gate operations. We also propose a multiple-bit design based on the nearest neighbor dipole-dipole coupling. Rabi population oscillation of an excitonic two-level system in an isolated single In xGa1-xAs quantum dot is manifested by quantum wave function interferometry in the time domain, demonstrating a long lived coherence of zero-dimensional excitonic states and revealing the coherent population flopping under strong optical field. Phase-sensitive coherent gate operations on a single-dot exciton qubit are demonstrated.