Entangling dopant nuclear spins using double quantum dots

Lead Research Organisation: University of St Andrews
Department Name: Physics and Astronomy

Abstract

Quantum mechanics has led to a deep and profound understanding of the electronic and optical properties materials, which has underpinned the technological revolution of the past century. Yet, there are key elements of quantum mechanics, specifically ideas such as 'coherent superposition' and 'entanglement', which have still to be harnessed directly in a technological application. With our improving ability to control smaller and smaller devices, with ever greater precision, we begin to enter a regime where such concepts can evolve from abstract 'thought experiments' to phenemona exhibited by real devices. Sufficiently controlled, superposition and entanglement will enable a new set of technologies - termed Quantum Technologies (QTs)- which offer major and fundamental improvements over certain existing technologies. Examples include ultimately secure communication, enhanced sensors, and 'quantum' computers able to solve problems that are simply intractable on any existing computer today.

Silicon devices have demonstrated quantum bit (qubit) characteristics which make them extremely promising for future QTs. As for most potential QT platforms, the next key step is identifying ways to scale up control and interactions between qubits, and, as seen when comparing different QT approaches, there is a compromise between using 'natural' quantum systems such as those based on atoms, and 'artificial' ones such as those based on superconducting circuits or quantum dots.

This project will bring together both such approaches, as is possible within a silicon-based architecture, in order to benefit from their respective advantages. We will use the uniquely long coherence times of donor spins in silicon (which can be as long as hours), with the tunable control of quantum dots in which entangled singlet and triplets are natural basis states. In doing so, we will demonstrate a scalable method to entangle very long-lived quantum bits in silicon, which will enable future applications in metrology and quantum computers.

Publications

10 25 50
 
Description 1. oscillatory coupling between donors in silicon, as a function of separation.

Using an intuitive model we were able to demonstrate that the interaction between the electron spins associated with donors - defect atoms substituted into the silicon lattice, oscillates rapidly with separation of donors. This makes control of this interaction difficult, and this makes building a quantum gate from this interaction challenging.

2. A new architecture for silicon based quantum computing. To overcome the difficulties with oscillatory interactions, we devised a new way to build quantum gates in silicon that is immune to differences in the interaction. These are so-called adiabatic gating strategies. We have proposed a way that these can be used in a large scale "surface code" architecture.

3. We have proposed that a new material - Germanium - may have advantages over silicon in hosting a dopant based quantum computer. This involved using multi-valley effective mass theory to show that the energy splitting donors can be tuned by many orders of magnitude more than donors in Si.
Exploitation Route Our theory blueprint can be used by our experimental partners to build new architectures for quantum gates.
Sectors Digital/Communication/Information Technologies (including Software),Electronics

 
Description Cambridge 
Organisation University of Cambridge
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Predicted exchange coupling between donors in silicon, and between donors and dots in silicon.
Collaborator Contribution The partners are manufacturing devices that will test the theory and lead to a small scale computing device.
Impact 2014 PRB paper (Pica et al) submitted as outcome was inspired by discussions with partners on donor-dot problem.
Start Year 2012
 
Description Soton 
Organisation University of Southampton
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Predicted exchange coupling between donors in silicon, and between donors and dots in silicon.
Collaborator Contribution The partners are manufacturing devices that will test the theory and lead to a small scale computing device.
Impact 2014 PRB paper (Pica et al) submitted as outcome was inspired by discussions with partners on donor-dot problem.
Start Year 2013
 
Description UCL 
Organisation University College London
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Predicted exchange coupling between donors in silicon, and between donors and dots in silicon.
Collaborator Contribution The partners and manufacturing devices that will test the theory and lead to a small scale computing device.
Impact The paper submitted as an outcome was generated following discussions with the partner.
 
Description Silicon Quantum Electronics Workshop 2016 - talk 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I gave a talk at the international conference, held in Delft Netherlands "Silicon Quantum Electronics Workshop 2016".
Year(s) Of Engagement Activity 2016
URL https://qutech.nl/events/siliconworkshop2016/