Coherent two-colour manipulation of a single QD-confined spin
Lead Research Organisation:
University of Cambridge
Department Name: Physics
Abstract
InGaAs quantum dots (QDs) give a very strong interface between a confined spin and well-defined optical modes. Here, we develop an all-optical technique for performing coherent control of this single spin, using a stimulated Raman process. This technique incorporates the flexibility of a direct microwave drive between the two Zeeman-split spin states with the speed of an optical scheme. We demonstrate full control over the rotation axis of the spin on the Bloch sphere, alongside a single-rotation fidelity of 97%, equalling that expected using conventional spin control techniques. Combining this frequency-selective, resonant control technique with a narrowed nuclear spin bath allows us to perform coherent operations well beyond the bare coherence times for this system, and means that we can look ahead to performing control of individual nuclear spins through their coupling to the confined central spin.
Organisations
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509620/1 | 01/10/2016 | 30/09/2022 | |||
| 1948685 | Studentship | EP/N509620/1 | 01/10/2017 | 31/03/2021 | Jonathan Bodey |
| Description | Self-assembled quantum dots (QDs) constitute the field-leading source of single photons, making them highly promising candidates for nodes of a quantum network. This application requires quantum control of a single (electron or hole) spin confined to the QD. This work has developed a new technique for manipulating a confined spin, achieving highly sophisticated control which operates at high-fidelity. In particular, this technique dramatically surpasses the sophistication of the previous state of the art, allowing arbitrarily complex pulse sequences to be designed. This has allowed us to protect a known quantum state, written into an electron spin superposition, for much longer than it would otherwise survive - using a technique known as spin locking. In addition, advance spin control has also allowed us to move beyond electron spin control and towards quantum control of the nuclear spins which make up the QD. Quantum states of the nuclei have much longer coherence times than for the electron, making them extremely desirable as an in-house memory for the electron. Using our control technique we have performed the first quantum manipulation of nuclear states in a self-assembled QD. This result opened the floodgates for experiments involving the nuclear spins. The first of these involved writing a single collective spin flip - a magnon - onto the nuclei, by driving them through the electron using our advanced spin control technique. Next, we were able to detect the hyperfine shift on the electron spin resonance (ESR) associated with this magnon by measuring the ESR with an accuracy of 2 parts per million. This write-detect protocol will be useful for exploiting the nuclear spins. Following this, we used the collective magnonic modes to probe the state of the nuclear spins. By driving these modes as we perturbed the system from its equilibrium configuration, we were able to measure the emergence of correlations consistent with a dark state, made up of 30,000 nuclear spins. |
| Exploitation Route | These results constitute a watershed achievement in the study of self-assembled QDs, and in the development of quantum networks in general. Next steps include moving towards high-fidelity nuclear state control, which would allow quantum simulation and quantum state transfer. |
| Sectors | Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software) |
| URL | https://www.joh.cam.ac.uk/index.php/physicists-get-thousands-semiconductor-nuclei-do-quantum-dances-unison |