Quantum Multiplexer

Lead Research Organisation: University of Cambridge
Department Name: Engineering


The split gate transistor was invented 22 years ago and has ben in wide-spread use ever since in the investigations of the fundamental physics of electron transport in low-dimensional structures. At most a few such transistors have ben used in very small circuits. We have devised a way of making over 1000 split gate devices on the same chip and the way to bias each gate, while needing only 40 contacts to read out the transport properties of the entire array. This advance will greatly accelerate both the physics investigations and the exploration of new device concepts, taking fully into account a statistical analysis of the results as a function of the intrinsic fluctuations from gate-to-gate.

Planned Impact

The following is abstracted from the attached Impact Statement. We note: (i) The quantum multiplexer is likely to give a major boost to areas as diverse as metrology, quantum computing, quantum information processing, cryptography and the basic physics as well. It will be a flexible research tool capable of being engineered into a useful general purpose device. It represents the first major advance since the original slit-gate transistors and the following experiments involving a few such gates. There is an enormous range of possible experiments on devices, circuits and statistical physics that will be enabled. It is the quantum version of a gate array, the classical version of which is in very widespread use in conventional electronics. The modern ITEC industry has a multi-$T annual budget. (ii) Getting a fully working multiplexer with associated modelling and simulation capability will require us to prove a number of points that are just beyond today's state-of-the-art, in particular the handling of many interacting potential wells as we set the gates to some agreed 'zero'. The organisation of this process may well have spin-offs into combinatorial optimisation more generally. (iii) Although many of the quantum applications in IT may be some way off, there is an immediate application in quantum metrology which has been identified and we will be working jointly with NPL on this aspect. The quest to achieve adequate accuracy for counting electrons as a measure of the current needs to be improved by 2-3 orders of magnitude, and the multiplexer is certain to give a contribution to that improvement: just how much remains to be seen. (iv) The training opportunities for both the post-doc and the research student are broad and highly advantageous. They will be exposed to growth, fabrication, design, test, and the use of low temperatures and high magnetic fields. The link with NPL will show how research can be focussed to an identified end-goal. The physics aspect is at the forefront of quantum transport of electrons in semiconductors, and may open up new areas in statistical physics. This will interest many international laboratories and give the two new researchers world-wide exposure. (v) This project highlights the links between physics and engineering in this subject and will make a good case study for widespread dissemination. We intend to use the work on outreach programmes within Cambridge, as we attract more STEM students to the university. (vi) There are important possibilities for producing, capturing and exploiting new intellectual property. The investigators all have experience of this in academia and in industry, both start-ups and large companies. If the multiplexer catches on in the way the original split-gates did there will be a business in producing and selling these as R&D samples.


10 25 50
Description We have established how to make a multiplexer, and have made 256 split gate arrays. We have initial results that will allow the statistics of multiple gates to be more effectively collected. We have measured quantum interaction effects in many devices allowing statistical analysis of how these phenomena change with the measured confining potential. We are examining the methodology for zeroing all the gates simultaneously. A simulation tool is being developed.

H Al-Taie, L W Smith, B Xu, P. See, J P Griffiths, H E Beere, G A C Jones, D A Ritchie, M J Kelly and C G Smith, 'Cryogenic on-chip multiplexer for the study of quantum transport in 256 spl
Exploitation Route Quantum signal processing, and information processing.

Quantum circuit design and evaluation for manufacture.

Metrology. To be decided, but are working closely with NPL in metrology
Sectors Electronics

Description EPSRC
Amount £745,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 11/2015 
End 10/2018
Title Automatic extraction of 1D subband energy 
Description A program was developed to deduce the 1-D subband spacing from 2D grey scale plots as a function of source drain bias and gate voltage. Usually the information is extracted by hand and eye, but because of the large amount of data this was time consuming. 
Type Of Material Data analysis technique 
Provided To Others? No  
Impact A. A. J. Lesage, L. W. Smith , H. Al-Taie, F. Sfigakis, P. See, J. Griffiths, I. Farrer, G. A. C. Jones, D. Ritchie, M. J. Kelly and C. Smith, "Automated data extraction from large numbers of quantum devices" submitted to Applied Physics Letters. 
Description NPL 
Organisation National Physical Laboratory
Country United Kingdom 
Sector Academic/University 
PI Contribution NPL have a parallel programme looking at quantum pumps for metrology and they think they will need a form of multiplexer to achieve the current levels for accurate measurements. We compared experiences on the design. fabrication and evaluation of our multiplexers.
Collaborator Contribution The same in reverse.
Impact Continued collaborations.
Start Year 2011
Description 10th International Workshop On Low Temperature Electronics 75, (2013) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Allowed us to set up links to theoreticians working in the field.

The link with theory resulted in a joint paper submission in 2014
Year(s) Of Engagement Activity 2013
URL http://arxiv.org/abs/1407.5806