Integrated superconducting nanobridge fast readout electronics for single photon detector arrays

Our objective is to develop nanobridge Josephson junction superconducting circuits (based on single flux quantum (SFQ)
design) for high bandwidth, low noise digital signal processing (DSP) of signals from single photon detector arrays (in
particular SSPD (superconducting single photon detector) arrays) and assess their suitability for commercialisation.
SSPD arrays have many applications; as a fast, high efficiency, low noise detector for quantum key distribution, as a
component in quantum computing and for enhanced quantum imaging. The major hurdle to commercialisation of SSPD
array systems is the lack of suitable readout electronics able to process a large number of signals without significant heat
loading of the detector cold stage. SFQ readout offers a low power solution, enabling multiple pixels in a marketable,
mechanically cooled system. Nanobridge SFQ circuits for SSPD array readout are a new, undemonstrated alternative to
conventional tunnel junction SFQ circuits, with the advantage of predominantly single layer fabrication, smaller device size
and potential for integration on the same chip as the SSPD array

Nanobridge SFQ consists of a single layer pattern "written" via e-beam lithography (and some additional components
fabricated via a simple lithographic technique) which is scalable to large number of pixels and offers the potential for future
integration on a single chip with the SSPD.
* Expected route to market: The feasibility project will provide proof of concept for nanobridge readout electronics. The next
stage would be to develop full readout electronics based on this concept. This would then be suitable for commercial
development. In addition there would be further development of integrated SSPD and readout electronics on a single chip.
A direct route to commercialisation is via the GU James Watt Nanofabrication Centre spin-out company Kelvin
Nanotechnology. The team will engage with academic end users through the National Network of Quantum Technologies
Hubs.
* Size of market: The emerging quantum communications and infrared detection market has been closely monitored [1-4].
The value of the global quantum communications market is estimated to reach $1billion by 2018. In[3], DSTL report that
the quantum communications area is set to grow over the next 3 -10 years and quantum simulation and computing is set to
grow in the longer term with large scale systems estimated to be built around 2025 - 30. Quantum imaging, applied to
biomedical and military and security application is also expect to grow substantially in the 10 year time frame [4].
The successful output of this project will be suitable for development to serve all the above mentioned areas. The ability to
process large amounts of data at high speed will be key as quantum based systems increase in complexity over the next
15 years. Therefore this work has the potential to realise significant impact and growth.
* How to explore market potential: In this feasibility project, the final part of the project will involve an assessment of the
success of this work and the application of it to various quantum technology areas. A report detailing the findings of the
project will be produced. In particular, describing suitability of nanobridge SFQ for producing a commercial, bench-top,
multi-pixel single photon detector array system. There is no competitor in Nanobridge SFQ electronics for SSPD array
readout, so the UK would gain an advantage in exploiting future market potential.
The output of the project will be a fully characterised key component of the nanobridge SFQ readout electronics (dc to SFQ
converter). This will be exploited in the following ways:
* Report detailing findings of feasibility study and a proposal of the next stages of development of system for commercialisation. It is expected that these would include fabrication of other components of the circuity (transmission
lines, buffers etc.), scaling of design for multiple pixels, and integration on single chip with SSPD array. The report will be
circulated to key stakeholders.
* Publication of results in leading international journal and international conference within a year of the project end.
* Further development, building on successful proof of concept, potentially co-funded by NPL via the NMS (National
Measurement System) programme.
* Potential commercial exploitation via the spin-off fabrication company Kelvin Nanotechnology at Glasgow University.
References
[1] SECOQC White Paper on Quantum Key Distribution and Cryptography 2007, [2] ETSI White Paper of Quantum Safe
Cryptography and Security 2014, [3] Pritchard, Till UK Quantum Technology Landscape DSTL 2014, [4] IR Detectors
Surveying the Market Ahead Laser Focus World 7/2011, [5] Global Industry Analysts Quantum Cryptography Global Market
Report 2014