Electron spin state manipulation in quantum dot circuits with engineered g-factor for quantum memory and communication applications

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Currently, there is broad interest in harnessing properties of quantum objects for quantum computation and communication. Quantum computers are predicted to be exponentially more powerful than the classical counterparts for certain tasks, for example, for modeling complex chemicals like drugs, for solving optimization problems (e.g. flight schedules), and breaking encryption codes. Quantum communication promises absolutely secure information transfer between parties using entangled photons as a resource, whose inspection or manipulation by a third party cannot compromise the security of the message being sent. Eavesdropping on such a connection is fundamentally disallowed by the quantum physics law called “no-cloning” theorem.Photons are the ideal quantum entities for transferring quantum information encoded, for example, in their polarization states. On the other hand, because photons do not interact easily, it is hard to manipulate and store them. These are necessary functionalities for building long distance quantum networks. These restrictions can be eased by using a quantum interface between photons and single electron spins trapped in quantum dots (QD), because electron spin states are much easier to store, manipulate, and measure using demonstrated state of the art techniques developed at NRC.The process of quantum state transfer from a photon to an electron requires specially engineered quantum states to participate in the process. In particular, the valance band hole state should be split by an in-plane magnetic field, while conduction band electron spin up and spin down states should remain degenerate, i.e. have the same energy. In scientific terms, the electron g-factor (the proportionality coefficient between spin splitting energy and the magnetic field) should be close to zero. In this condition it is impossible to tell which of the electron spins is created, except through direct measurement of the spin. Therefore, a quantum superposition of spin states can be created by a photon of well-defined energy. The electron state created in this process maps out the photon quantum state. In other words, one bit of quantum information is transferred.The first step in achieving this spin-to-photon interface is to realize special quantum dots with g*~0. This constitutes the main goal of the proposed research. We will develop double quantum dot devices made from the engineered g-factor materials and explore their feasibility for quantum information transfer between photons and electron spins. The electron g-factor will be measured using single spin resonance techniques by monitoring current through a double quantum dot device tuned to the so-called spin-blockade regime. In this regime current is suppressed due to the Pauli exclusion principle, which prevents a mobile electron from tunneling from one dot to the other dot if it already contains an electron of the same spin. Manipulation of spin states will be achieved by applying short microwave bursts and pulse sequences to the QD gates.In this project we tackle a small but critical component of a greater worldwide activity directed onto the development of secure quantum networks. The necessary and lacking component is an effective spin to photon interface that would ease building efficient quantum memories and repeaters required for the distribution of entanglement in quantum networks. The results of this work will be easily adopted by a growing number of start-up companies and centers interested in quantum technologies.