Ultrafast optical control of entanglement between two quantum-dot spins

Abstract

The interaction between two quantum bits enables entanglement, the two-particle correlations that are at the heart of quantum information science. In semiconductor quantum dots much work has focused on demonstrating single spin qubit control using optical techniques. However, optical control of entanglement of two spin qubits remains a major challenge for scaling from a single qubit to a full-fledged quantum information platform. Here, we combine advances in vertically-stacked quantum dots with ultrafast laser techniques to achieve optical control of the entangled state of two electron spins. Each electron is in a separate InAs quantum dot, and the spins interact through tunneling, where the tunneling rate determines how rapidly entangling operations can be performed. The two-qubit gate speeds achieved here are over an order of magnitude faster than in other systems. These results demonstrate the viability and advantages of optically controlled quantum dot spins for multi-qubit systems.Semiconductor quantum dots (QDs) were among the first candidates proposed for solid-state qubits 1 . Self-assembled InAs QDs are a versatile physical platform, because they are epitaxially grown in a semiconductor wafer and can be fabricated into a monolithic architecture containing both electronic 2 and photonic 3 circuit elements. Individual QDs themselves can be organized into more complex "molecules" in one, two, and three dimensions. 4 With these engineering advantages, one can envision building an entire quantum network with the scalability and stability of a solid-state system.The elementary optical excitation of a QD, the exciton, has a resonance frequency in the optical regime, giving QDs a great speed advantage over nuclear spins (radio frequency) or electron spins (microwaves). With the giant optical dipole of a semiconductor quantum dot, quantum operations can be performed at a terahertz rate or faster 5 . Coherent manipulations of pure exciton qubits were the first quantum gate demonstrations in the solid state 6,

Coulomb interaction signatures in self-assembled lateral quantum dot molecules

“…QDMs are also of interest as a component of optoelectronic devices because the molecular coupling can be controlled by electric and magnetic fields. Consequently, QDMs are a promising material for single spin/charge optoelectronic devices 5 including quantum computing devices. 6 In the past decade, most research related to QDMs has focused on vertically stacked QDMs (VQDMs).…”

Complete quantum control of exciton qubits bound to isoelectronic centres

“…The physics of ICs is reminiscent of quantum dots (QDs), a system widely studied for quantum computation [2][3][4][5][6] . Their semiconductor host allows one to take advantage of convenient optical selection rules for spin initialization, manipulation and readout; to exploit dynamic charge doping, electrical coherent control 7 and device integration; and to fabricate high quality Bragg reflectors and cavities.…”

Scalable qubit architecture based on holes in quantum dot molecules

“…1 Spins confined in III-V semiconductor self-assembled quantum dots (QDs) have received a great deal of attention because they interact strongly with light and provide the opportunity for ultrafast all-optical implementation of logic operations. [2][3][4][5] There has been dramatic progress in the initialization, coherent manipulation and readout of single spins in GaAs and InGaAs QDs, [6][7][8][9][10][11][12][13] but many challenges to the creation of a scalable quantum logic device based on optical control of single spins remain. One serious obstacle is the natural inhomogeneous distribution of energy levels in a quantum dot ensemble.…”