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Details of Grant 

EPSRC Reference: EP/M508330/1
Title: Integrated superconducting nanobridge fast readout electronics for single photon detector arrays
Principal Investigator: Romans, Dr EJ
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: London Centre for Nanotechnology
Organisation: UCL
Scheme: Technology Programme
Starts: 01 June 2015 Ends: 31 May 2016 Value (£): 50,130
EPSRC Research Topic Classifications:
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Summary on Grant Application Form
The project will develop a compact, cryogenic readout for superconducting single photon detector SSPD arrays and assess

their suitability for commercialisation. The readout will be based on a superconducting single flux quantum (SFQ) circuit

where an input signal is converted into a series of quantised pulses that can be used for digital signal processing. The

building block of the SFQ circuits will be loops containing superconducting nanobridges that act as weak links displaying

the Josephson effect.

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.

The research that will be carried out University College London will involve the actual fabrication of the nanobridge SFQ

circuits. The nanobridge circuits will be fabricated using e-beam lithography and lift-off of superconducting thin films

deposited in a cleanroom facilty. Initial work will be be needed to determine the electrical parameters of nanobridges of

various dimensions so that a full circuit model can be developed and tested. A complete SFQ device design can then be

fabricated and tested and assessed by the project partners at NPL. In order to couple the fast pulse from an SSPD to the

SFQ an input coil circuit will be needed to amplify the current. We will design and fabricate suitable multiturn input coils with

appropriate terminating resistors. These will be tested by the project partners at NPL. We will then fabricate fully integrated

devices (input coil and SFQ devices) which will be tested and evaluated at NPL, initially with external electrical input

pulses, but eventually with real SSPD signals from devices supplied by project partners at Glasgow University.
Key Findings
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Potential use in non-academic contexts
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