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QUANTUM MEASUREMENTS

 

Program Manager
Prof Robert Clark - University of New South Wales

Quantum Measurement Researchers
Staff
Dr Andrew Ferguson

Mr Bob Starrett (NML Manager)
Mr Dave Barber (Cryogenics Manager)

Students
Mr Marc Ahrens (PhD), Ms Nadia Court (PhD), Mr Dane McCamey (PhD),
Mr Victor Chan (PhD), Mr Mladen Mitic (PhD

Collaborating Centre Researchers:
Dr Søren Andresen - University of New South Wales
Dr Rolf Brenner - University of New South Wales
Dr Fay Hudson - University of New South Wales
Prof Andrew Dzurak - University of New South Wales
Prof Michelle Simmons - University of New South Wales
A/Prof Lloyd Hollenberg - University of Melbourne

Program Description:
This program has two objectives:
(a) to develop single spin detection techniques for quantum computer read-out
(b) to maintain an underpinning capability in measurement of quantum electronic devices.

 

 

Figure 1: A twin-SET device for single electron charge motion detection.

 

Several approaches are being investigated for single spin detection. The main approach involves the detection of electron charge transfer using a highly charge sensitive single electron transistors (SETs), which which is used to read out the spin state of a single electron in a Si-based QC (in the case of a nuclear spin QC the phosphorous' nuclear spin is transferred to its donor electron). ). This is possible due to the extremely high sensitivity of an SET to local charge density, which makes it the world's most sensitive electrometer. The main type of SET being studied in this program at present is based on the Al/Al2O3 material system. The image below shows two such SETs in an integrated structure we have fabricated, which has been designed at the Centre for its high sensitivity to the type of read-out signal expected in a Si QC. The data shows the measured conductance of one such device as a function of a controlling gate voltage. Note the sharp peaks in the conductance, which are typical of SET devices, and which give rise to their high sensitivity. This research involves extremely low noise electrical measurements using sophisticated cryogenic dilution refrigerators in the National Magnet Laboratory to achieve the millikelvin temperatures required.

Extensive theoretical modelling of quantum state control and read-out in these devices is performed through collaborative programs with the universities of Melbourne and Queensland. Alternative techniques for single spin readout are being developed, including a major collaboration on scanning probe magnetic resonance force microscopy (MRFM) techniques with researchers at Los Alamos National laboratory, and SQUID based spin detection with colleagues at University of Melbourne.

In addition to the focussed objective of single spin readout, the Centre maintains an underpinning capability in the measurement of quantum effect devices. A detailed understanding of electron transport through confined geometries, and how this is governed by the laws of quantum physics, is vital if the properties of nanostructures are to be exploited in the next generation of electronics.

 

 


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