Quantum Key Distribution at Terahertz Frequencies

The possibility of developing quantum computing machines that can break the widely used public key cryptosystems has required us to look into new solutions for scenarios where long-term data security is needed. Quantum key distribution (QKD) is a technique that would provide the required level of data security but has so far been limited to fixed optical implementations. This project will explore, both experimentally and theoretically, the use of Terahertz frequencies to enable a wireless implementation of QKD.

<p>Quantum key distribution (QKD) is among the enabling techniques for providing such a level of data security. Being reliant on few-photon communications, it is generally believed that implementing QKD in the optical domain is the most straightforward solution.</p> <p>However restricting this technology to the optical domain could make it more difficult to realise QKD when mobility and wireless access are required. This motivates us to consider using carrier signals at lower THz frequencies to enable wireless implementations of QKD. The terahertz regime offers a feasible, but as yet unexplored, regime of operation, where QKD can, in principle, be implemented [1]-[2].</p> <p>This interdisciplinary theory-experimental project has the ambitious goal of demonstrating THz QKD systems for the first time. This will be enabled by collaboration between our two well-established theory and experimental groups in, respectively, quantum communications and THz technologies with the support of Cambridge University, and will be the first experimental demonstration of QKD in the School. In this project, we will implement a special class of QKD protocols known as continuous-variable QKD (CV QKD) [3]. Such protocols rely on generating coherent states with controlled phase and amplitude values of the electric field to encode the information, and homodyne/heterodyne detection at the receiver.</p> <p>Luckily, our recent work with THz quantum cascade lasers (QCLs) has enabled us to lock the THz frequency to a near infra-red comb operating around 1550 nm. This allows full control over the amplitude and phase of the QCL. Furthermore, we are able to independently measure the amplitude and phase of the locked QCL by coherent detection, which is a key requirement for CV QKD.</p> <p>The objectives of this project are:</p> <ol> <li>To investigate the coherent detector performance both theoretically and experimentally to understand the detector noise characteristic and the operating conditions required for quantum secure operation;</li> <li>To develop theoretical techniques that account for imperfections in the experimental setup to give us a realistic picture of what is achievable with existing setups and how they must be improved to enable THz QKD under controlled lab conditions;</li> <li>To use locked sources to produce THz pulses suitable for QKD, with arbitrary control over the amplitude and phase;</li> <li>To implement a QKD protocol over a THz channel with controlled temperature and shielding conditions; and</li> <li>To experimentally explore the operational limits of the system, and theoretically investigate its performance in satellite links.</li> </ol> <p>References:</p> <p>[1] Carlo Ottaviani, Matthew J. Woolley, Misha Erementchouk, John F. Federici, Pinaki Mazumder,&nbsp;Stefano Pirandola, Christian Weedbrook, &quot;Terahertz Quantum Cryptography,&quot; in IEEE Journal on Selected Areas in Communications, vol. 38, no. 3, pp. 483-495, March 2020.</p> <p>[2] Z. Wang, R. Malaney and J. Green, &quot;Inter-Satellite Quantum Key Distribution at Terahertz&nbsp;Frequencies,&quot; ICC 2019 - 2019 IEEE International Conference on Communications (ICC), Shanghai,&nbsp;China, 2019, pp. 1-7.</p> <p>[3] Eleni Diamanti and Anthony Leverrier, &ldquo;Distributing Secret Keys with Quantum Continuous&nbsp;Variables: Principle, Security and Implementations,&rdquo; Entropy 17, 6072-6092, 2015.</p>

<p>Formal applications for research degree study should be made online through the&nbsp;<a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees">University&#39;s website</a>. Please state clearly in the Planned Course for Study section that you are applying for&nbsp;<em><strong>EPSRC DTP Engineering &amp; Physical Sciences</strong></em>, in the research information section&nbsp;that the research degree you wish to be considered for is&nbsp;<strong><em>Quantum Key Distribution at Terahertz Frequencies</em></strong>&nbsp;as well as <a href="https://eps.leeds.ac.uk/electronic-engineering/staff/495/professor-mohsen-razavi">Professor Mohsen Razavi</a>&nbsp;as your proposed supervisor and&nbsp;<em><strong>in the Finance section, please state that the funding source you are applying for is EPSRC Quantum Technologies&nbsp;Doctoral Training Studentship</strong></em>.</p> <p>If English is not your first language, you must provide evidence that you meet the University&#39;s minimum English language requirements (below).</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p> <p>Applications will be considered on an ongoing basis. &nbsp;Potential applicants are strongly encouraged to contact the supervisors for an informal discussion before making a formal application. &nbsp;We also advise that you apply at the earliest opportunity as the application and selection process may close early, should we receive a sufficient number of applications or that a suitable candidate is appointed.</p> <p>Please note that you must provide the following documents at the point you submit your application:</p> <ul> <li>Full Transcripts of all degree study or if in final year of study, full transcripts to date</li> <li>Personal Statement outlining your interest in the project</li> <li>CV</li> </ul>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<p>A highly competitive EPSRC Quantum Technologies Doctoral Training Partnership Studentship offering the award of fees, together with a tax-free maintenance grant of &pound;19,237 per year for 3.5 years.&nbsp; Training and support will also be provided.<br /> <br /> This opportunity is open to UK applicants only.<br /> <br /> Please refer to the&nbsp;<a href="https://www.ukcisa.org.uk/">UKCISA</a>&nbsp;website for&nbsp;information regarding Fee Status for Non-UK Nationals.</p>

<p>For further information regarding your application, please contact Doctoral College Admissions by email to&nbsp;<a href="mailto:phd@engineering.leeds.ac.uk">phd@engineering.leeds.ac.uk</a></p> <p>For further information regarding this project, please contact Professor Mohsen Razavi by email to&nbsp;<a href="mailto:M.Razavi@leeds.ac.uk">M.Razavi@leeds.ac.uk</a></p> <p>For information about Quantum Technologies or the Bragg Centre for Materials Research, please email&nbsp;<a href="mailto:BraggCentre@leeds.ac.uk">BraggCentre@leeds.ac.uk</a>.</p>