Creating, detecting and exploiting quantum states of light

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of Engineering and Physical Science

Abstract

The last decade has seen a world-wide expansion in investigation into quantum states of light. Much of the expansion in this subject area has been stimulated by the emergence of quantum cryptography or quantum key distribution (QKD) / first proposed in 1984 - which offers unconditionally secure information transport guaranteed by quantum-mechanical laws. Whilst QKD remains a fertile subject of exciting laboratory and field research, experimental progress in free-space and optical fibre transmission media have taken quantum cryptography to the fringes of commercial exploitation and real-world application. Concurrently, a number of other developments in quantum information research have also been highly significant, such as quantum computing algorithms that, if realised, would make today's public-key based data security system obsolete. The building blocks, or quantum components, of these quantum-based systems require considerable research effort and this is the subject matter of this proposal. Significantly and perhaps in a more short-term manner, a number of these components will be utilised in other applications outside the quantum information processing sphere; these applications include including low-light level communications (eg as proposed in the NASA Mars Communications Programme), in remote sensing, imaging and quantum-based metrology.This Platform Grant application from the Heriot-Watt group centres on leading edge research into the creation, detection and exploitation of the quantum states of light. This project will be used to make strategic decisions regarding research in these fast-moving fields. At the time of application, a number of exciting projects have been highlighted for investigation, although these projects are not meant to represent a comprehensive and exclusive list of research topics. Some areas worth immediate investigation include prototype quantum devices such as quantum dots for entangled photon pair production; or quantum imaging in remote sensing, or single-photon sources constructed from carbon nanotubes. Whilst this grant will not provide the full resources for long-term investigations into all these areas, this project will permit rapid start-up and allow the group to collaborate more effectively with other groups, including overseas researchers.
 
Description Imaging and sensing with quantum states of light
This was a key goal in the original Platform Grant proposal and remains an area of keen international interest with significant potential for commercial exploitation. The Platform Grant assisted the lead-up to another responsive mode project "Quantum Imaging" collaboration with Glasgow and Strathclyde (2009). It provided flexibility whilst this other funding was secured, allowing the team to have a running start at this research, allowing better continuity of staff (initially funding Dr Ryan Warburton). Overall, this work has progressed well, allowing a number of international firsts to be obtained: demonstration of quantum correlations in position and momentum (and intermediate bases) in full-field; examination of new detector technology in quantum imaging; and investigation of super-resolution due to quantum entanglement. The Platform Grant has also given us the freedom to examine complementary subject areas, such as the demonstration of high dimensional entanglement, this, rather esoteric-sounding research area may ultimately present a route to exploitable technologies such as large-alphabet quantum cryptography. In such communication schemes, a single encoded photon can contain multiple bits in a secure encryption key, boosting data transmission rates dramatically. Research on large alphabet QKD has been initiated by our team and is continuing assisted by partial support of the Platform Grant.
Groundbreaking efforts in single-photon time-of-flight ranging and imaging by our team have been boosted by partial support from the Platform Grant. Since the start of the Platform Grant, progress in this area was sustained after EMRS Defence Technology Centre funding came to an end, permitting a full demonstration of kilometre imaging from non-cooperative targets. Later the Platform Grant helped initiate work by Buller and Hadfield on single-photon depth imaging at the challenging and strategically important ?~1550nm band using superconducting nanowire detectors, work that has proved extremely successful, achieving objectives beyond initial expectations. Our success in long-range time-of-flight imaging has led to further projects funded by non-EPSRC routes (see funding summary below), eg EU Framework Seven (MiSPIA - using of SPAD arrays), DSTL (underwater imaging) and CEOI (forest canopy analysis). The Platform Grant has helped retain key staff (notably Dr Aongus McCarthy), and stimulated ambitious research that could not have been attempted without the Platform Grant.
Prototype quantum devices and non-traditional semiconductors for single photon generation
Four goals were identified in the previous Platform Grant: embedding a superconducting nanowire in a micro-cavity to enhance the quantum efficiency; developing a tunable micro-cavity technology around quantum dots for efficient photon state generation; manipulating the symmetry of single quantum dots with external strain to create source of on-demand entangled photon pairs; and performing quantum state tomography on quantum dots with David Gershoni (Technion, Israel). Each of these has proved successful and has opened new opportunities to realize practical quantum photonic technologies. By fabricating a superconducting nanowire on oxidized silicon with a thickness optimized for telecom wavelength photons, we created a modest cavity effect which significantly enhanced the detector's quantum efficiency. Furthermore, we have successfully developed a cavity with a high Q-factor, reasonably small mode volume, open access, spatial and spectral tunability that is compatible with cryogenic temperatures [ ]. We have made a proof-of-principle demonstration with quantum dots [ ], but the cavity platform is generic and applicable for any quantum emitter. However, the use of a high-Q cavity for increasing the efficiency of light-matter interaction with quantum emitters is inherently narrow-band, and therefore not so useful for systems with more than 2 quantum levels that are not monochromatic (e.g. the 3-level system useful for quantum information storage and processing and the 4-level system required for generation of entangled photon pairs in a quantum dot). Motivated by this and other limitations of cavity structures, Gerardot is developing broadband optical antennas to increase the light-matter interaction efficiency in the solid-state. Initially supported by the Platform Grant and later by a Challenging Engineering grant, this programme aims to fabricate devices with efficiencies sufficient for realistic applications. Regarding the use of an externally applied strain field, we have recently taken an important step by fully characterizing the response of single particles in quantum dots to uniaxial strain using Coulomb blockade. This result underpins the recent ERC Starting Grant award and enables us to apply the flexible in situ strain tuning technique for desired applications such as entangled photon generation, obtaining indistinguishable photons from multiple emitters on the same-chip for scalable quantum technologies, and reaching the ultimate quantum coherence limit by engineering single particle wave-functions. Finally, in collaboration with Gershoni at the Technion, we have uncovered a promising new state for storing and processing quantum information by performing quantum state tomography on a 'dark' exciton in a quantum dot. Notably, we strategically chose not to invest strongly in developing in-house capabilities in non-traditional semiconductors (e.g. carbon nanotubes and diamond defect centres) due to our very successful investigation and exploitation of quantum dots for single photon generation and quantum information manipulation.
Overall, the Platform Grant has permitted the following: (a) the establishment of inter-University and industrial collaborations providing a pathway to impact and mechanism for dialogue between researchers and beneficiaries via the support and retention of grant-funded researchers who, in most cases, were later funded by other means; (b) the flexibility to support in-depth exploration of topics: looking for new areas of high impact research outside existing responsive mode funding, by performing preliminary experimental work and detailed analysis; (c) the support of world-class visiting researchers and exchange visits by our own group members to stimulate new ideas; and (d) support for dissemination of the work supported by the Platform Grant.
Exploitation Route Much of the work has been continued via Platform Grant renewal (203-2017) and also by the National Quantum Technology Programme, via the QT Hubs.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Electronics,Environment,Security and Diplomacy,Transport

 
Description EPSRC Platform Grant - Creating, detecting and exploiting quantum states of light
Amount £1,005,002 (GBP)
Funding ID EP/K015338/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2013 
End 06/2017
 
Description UK Quantum Technology Hub for Quantum Communications Technologies
Amount £24,093,966 (GBP)
Funding ID EP/M013472/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 11/2019
 
Description UK Quantum Technology Hub in Quantum Enhanced Imaging
Amount £23,061,154 (GBP)
Funding ID EP/M01326X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 12/2014 
End 11/2019