[Paper Review] Quantum optical interface for gate-controlled spintronic devices

Hans‐Andreas Engel, Jacob M. Taylor+2 more|arXiv (Cornell University)|Dec 29, 2006

Quantum and electron transport phenomena3 citations

TL;DR

This paper proposes a hybrid quantum system that coherently couples gate-defined semiconductor quantum dots to optically active self-assembled quantum dots (SAQDs) via capacitive coupling or electron tunneling, enabling optical control and readout of spin qubits. The key contribution is a scalable architecture for quantum information processing with coherent spin-photon entanglement and high-fidelity spin transfer, achieving infidelity <10⁻⁴ and spin-photon entanglement error ≤5%.

ABSTRACT

We describe an opto-electronic structure in which charge and spin degrees of freedom in electrical gate-defined quantum dots can be coherently coupled to light. This is achieved via electron-electron interaction or via electron tunneling into a proximal self-assembled quantum dot. We illustrate potential applications of this approach by considering several quantum control techniques, including optical read-out of gate-controlled semiconductor quantum bits and controlled generation of entangled photon-spin pairs.

Motivation & Objective

• To overcome the lack of optical access in gate-defined quantum dots, which limits quantum control and scalability.
• To enable optical readout and manipulation of spin qubits in semiconductor quantum dots using nearby optically active self-assembled quantum dots (SAQDs).
• To develop a scalable architecture combining electrical control of gate-defined dots with optical access via SAQDs for quantum information applications.
• To achieve coherent spin-photon entanglement and high-fidelity spin transfer between electronic and photonic degrees of freedom.

Proposed method

• Utilizes an inverted GaAs/AlGaAs heterostructure with a 2DEG and embedded InAs self-assembled quantum dots (SAQDs) grown during the GaAs layer deposition.
• Employs capacitive coupling between gate-defined quantum dots and SAQDs to shift the SAQD excitonic transition frequency based on the charge state in the gate-defined dot.
• Uses electron tunneling from gate-defined dots into proximal SAQDs to mediate coherent spin-photon coupling.
• Employs resonant photoluminescence or differential transmission to detect spin states via Stark shifts induced by local electric fields.
• Applies a conditional optical scheme for entangling two remote spin states via photon detection, with success probability η²/4.
• Analyzes error sources in spin-photon entanglement, including forbidden transitions, phonon decoherence, tunneling, and frequency mismatch, and estimates total error ≤5%.

Experimental results

Research questions

• RQ1 Can gate-defined quantum dots be coherently coupled to light via interaction with nearby self-assembled quantum dots?
• RQ2 What is the fidelity of coherent spin transfer between gate-defined quantum dots and SAQDs via capacitive coupling or tunneling?
• RQ3 Can optical readout of spin states in gate-defined quantum dots be achieved with high efficiency and low infidelity?
• RQ4 What are the dominant error channels in generating and detecting spin-photon entanglement in this hybrid system?
• RQ5 Can this architecture enable scalable quantum computing and communication via optical interconnects between quantum dot registers?

Key findings

• The infidelity of coherent spin transfer between gate-defined quantum dots and SAQDs is less than 10⁻⁴ under typical parameters, indicating high-fidelity operation.
• The error in generating remote spin-photon entanglement is estimated at ≤5%, primarily due to forbidden transitions (≤1%) and frequency mismatch (1%).
• Capacitive coupling induces a Stark shift of ~20 μeV per kV/cm², enabling state-dependent optical detection of charge configurations.
• The scheme supports optical readout of spin qubits via differential transmission or photoluminescence, enabling fast and robust measurement.
• The system enables conditional generation of entangled photon-spin pairs with a success probability of η²/4, scalable via repeated attempts.
• The architecture allows for local spin probing in 2DEG systems, such as detecting spin polarization at edges due to the spin Hall effect.