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PhD Positions on Offer

Quantum Photonics

Partner: Toshiba Research Europe Ltd.

UCL co-supervisor: To be confirmed

Experimental Project

Main location of project: Toshiba Research Europe Ltd (Cambridge, UK)

Toshiba Research Europe Ltd (TREL) in Cambridge is developing quantum technologies based on superposition and entanglement that can be exploited for new applications in communications, sensing and computing. Their notable achievements in quantum photonics include the first LEDs for generating single photons[1] and entangled light[2], the first electrically driven system to teleport quantum states of light[3,4] and a device which can sort light into single and multi-photons[5]. They are also at the forefront of research in quantum communications and are engaged in pilots of the technology in the UK, Europe and Japan.

A PhD project, funded by the EPSRC and TREL, is available in the Quantum Information Group at TREL, led by Dr Andrew Shields. The PhD will involve experiments on semiconductor devices and circuits that can be used to generate, manipulate and detect quantum states of light and explore their applications in quantum information technology.

The work is mostly experimental in nature and will involve the design, fabrication and characterisation of semiconductor photonic devices. Current work is focused on realising discrete components and photonic integrated circuits that can be applied to quantum key distribution, long distance quantum communications (quantum relays and repeaters), as well as quantum information processing. The candidate will have access to world leading facilities for quantum optical experiments at the Toshiba lab.

The successful applicant will join a large and vibrant team working in this area. The group has excellent links to other leading groups in the UK, through collaboration with the EPSRC Quantum Technology Hubs and CDTs, as well as in Europe and Japan, through several collaborative projects. A willingness and ability to travel globally would be an advantage.

The candidate should have a general understanding of semiconductor device physics and photonics, as well as an enthusiasm for experimental work. A top class degree in physics or a related engineering discipline is essential.

References

[1] Yuan et al, Science 295, 102 (2002).

[2] Salter et al, Nature 465, 594 (2010).

[3] Nilsson et al, Nature Photonics 7, 311 (2013).

[4] Stevenson et al, Nature Communications 4, 2859 (2013).

[5] Bennett et al, Nature Nanotechnology 11, 857 (2016).

Optical atomic clocks with 10-18 uncertainty

Supervisors: Dr Rachel Godun (NPL)

Main location of project: National Physical Laboratory, Teddington TW11 0LW

Experimental Project

Background and motivation

Recent innovations in the field of frequency metrology (Margolis, 2010 ) have enabled scientists to measure time and frequency with an accuracy approaching a part in 1018, continuing to make frequency the most accurately measured physical quantity. Many quantum technologies can benefit from this level of performance. For example, general relativity tells us that a height change of just 1 cm at the earth’s surface changes the gravity potential enough to cause frequency deviations at the level of a part in 1018. Atomic clocks working with this precision could thus be used as quantum sensors in surveying for gas and oil, and monitoring ocean currents and sea-level rise. Improved frequency stability of atomic clocks also leads to more accurate global navigation satellite systems and numerous space applications. The atomic clocks that enable these measurements are based on interrogating the frequency of an electromagnetic transition between two internal energy levels within an atom. The National Physical Laboratory runs the UK’s most accurate clocks, including one that is based on an optical transition in a single ytterbium ion (171Yb+) held in an rf Paul trap (see below). With this experimental apparatus we have created a table-top platform for exploring physics beyond the standard model. (Godun, et al., 2014)

MRes project

For practical purposes, it is desirable to reduce the averaging time required to reach statistical uncertainties at the 10-18 level. This averaging time depends on a number of factors, including: the stability of the laser interrogating the ‘clock’ transition, the coherence time of the trapped ions and the number of ions being probed. During the MSc project, the stability of the Yb+ clock will be fully characterised and improvements made to reduce the necessary averaging time. A student will be trained in understanding the requirements of optical atomic clocks and will work with lasers, vacuum systems, electronics and computer control.

PhD project

Following on directly from the MSc project, a full evaluation of the clock’s accuracy will be carried out, and new techniques employed to minimise any frequency offsets. To verify the clock’s performance, it will be characterised against other optical clocks locally and also compared with clocks across Europe (via optical fibre link) and across the world (via clocks on board the International Space Station). These international comparisons are essential to build confidence in optical clocks prior to a redefinition of the second, and the ability to reach accuracy at the part in 1018 in much shorter averaging times is a key step in enabling the uptake of optical clocks across a broad range of applications.

References:

[1] H. Margolis, “Optical frequency standards and clocks,” Contemporary Physics, vol. 51, pp. 37-58 , 2010.

[2] R. M. Godun, et al., “Frequency ratio of two optical clock transitions in 171Yb+ and constraints on the time-variation of fundamental constants ,” Physical Review Letters, vol. 113, p. 210801, 2014.

Fault tolerant silicon-based quantum processors

Partner: Quantum Motion Technologies Ltd.

Main location of project: UCL (London, UK)

UCL co-supervisor: Prof John J L Morton Experimental Project

Summary: Silicon-based approaches to quantum information processors offer advantages such as high qubit density, record qubit coherence lifetimes for the solid state, and the ability to leverage the advanced nanofabrication methods of CMOS technologies. This project will focus on the measurement of silicon quantum devices, including spin qubits based on donor atoms and/or quantum dots, measuring basic qubit properties, as well as single- and multi- qubit gate fidelities, to help validate and refine fault-tolerant architectures based on spin qubits in silicon. The project will also develop robust and scalable ways to read out and manipulate spin qubits. Collaborations with the project will include theoretical groups on the design of fault-tolerant quantum architectures in silicon as well as nano-fabrication facilities. There will be opportunities to learn about advanced nanofabrication techniques as well as to develop experience of quantum transport, reflectometry, coherent control and measurements an milliKelvin temperatures in a dilution refrigerator (see Figure 1).

Past work: The spins of donor atoms in silicon have record quantum coherence lifetimes for solid-state systems, being up to seconds for the electron spin [1] and hours for the nuclear spin [2]. Spins of single quantum dots and donors can be manipulated and controlled with high fidelity [3], and indeed both can be coupled together in CMOS-compatible silicon nanodevices [4] (see Figure 2). Stimulated by this great promise, a variety of promising architectures are being developed to enable scaling to larger numbers of spins [5,6].

Quantum Motion is a recent start-up founded by Professor Simon Benjamin (University of Oxford) and Professor John Morton (UCL), developing new technology aimed at creating a quantum computer based on silicon.

References

[1] Wolfowicz et al., Nature Nanotechnology, 8 561 (2013)

[2] Saeedi et al., Science 342 830 (2013)

[3] Veldhorst et al., Nature Nanotechnology 9, 981 (2014); Muhonen et al., Nature Nanotechnology 9, 986 (2014)

[4] Urdampilleta et al., Physical Review X 5, 031024 (2015)

[5] Li et al., arXiv:1711.03807 (2017)

[6] O’Gorman et al., NPJ Quantum Info 2, 15019 (2016)