Spotlight – How to... characterise and analyse materials with a quantum transport measurement system

Materials World magazine
,
1 Feb 2018
Nanonis Tramea

Dr Harriet van der Vliet*, Quantum Engineer at Oxford Instruments, Dr George Lengel, SPECS-TII Inc., and Dr Alessandro Pioda, SPECS Zurich GmbH, explain how quantum transport measurement systems, such as the Nanonis Tramea, facilitate research in device characterisation.

What is quantum computing?

The operation of quantum computers relies on the formation of quantum bits or qubits, where the state is not constrained to merely 0 or 1, as in traditional binary or classical computers. Instead, each bit of information is represented by the state of a quantum system, which can be in a superposition of multiple states simultaneously, allowing more complex data to be encoded on a single qubit. 

Why do we need new characterisation methods?

With the limit to classical computing power fast approaching, research in both academia and industry is focusing on novel materials and frameworks, with which to realise quantum computing.

There are a number of different ways of realising a quantum computer, but pioneering work on quantum dots – a quasi-zero-dimensional nanostructure that can confine single electrons, whose spin or charge degree of freedom can then be used to represent qubits – formed in semiconductors are one of the front runners. Quantum dots are a promising candidate as a building block for quantum information and computation.

A wide variety of methods to form qubits are being investigated in numerous research groups.

What is it used for?

SPECS Nanonis Tramea, a quantum transport measurement system, provides a new way of working that delivers precise and fast measurements. It is versatile and can handle different measurement methods compared to commonly used laboratory equipment. It is the only one of its kind currently on the market and therefore a leading example of how software-controlled, digitally integrated instruments with higher sampling rates can boost efficiency, producing high volumes of data in shorter times. This empowers pioneering scientists to benefit from Nanonis Tramea for research challenges which require high throughput, parallelisation or where sample lifetime is limited.

When Nanonis Tramea is combined with dilution refrigerators and a wide range of low and ultra-low temperature systems from Oxford Instruments, it leads to a powerful combination providing the ultimate efficiency for quantum transport researchers. Quantum transport measurements are widely used in characterising new materials and devices for emerging quantum technology applications such as quantum information processing, quantum computing and quantum sensors. The instrument includes the capability to communicate with and control Oxford Instruments integrated magnets and magnet and temperature control, offering full control of the whole experiment from a single optimised interface. 

With Nanonis Tramea you do not need to choose between high signal performance (at the cost of measurement speed) or fast data acquisition (suffering from lower resolution and higher noise) as the instrument guarantees both at the same time. For best-in-class research, software-based instruments are crucial, as they offer simpler signal handling and a much better workflow through a powerful and customisable user interface. Software and hardware are stable, providing reliability in a compact footprint.
Nanonis Tramea is safer than commonly used multi-unit equipment as there is no need to disconnect and reconnect cable – there is a single electrical ground and the software provides extensive options to avoid sample damage.

Nanonis Tramea can control eight inputs and outputs in the base configuration (expandable up to 24 inputs and 48 outputs) simultaneously in one user interface. This, combined with the lock-in amplifiers available in module upgrades, permits multiple samples to be measured at the same time in parallel, increasing the throughput of samples and the speed of device characterisation. As all of this functionality is housed within one unit, the communication speeds and the data acquisition times are shorter. Specifically, there is no need to incorporate slow bus connections between individual devices that traditional instruments rely on. 

Experiments to characterise materials

For many experiments, Nanonis Tramea is all that is required to perform the complete measurement and can be used when there are many more qubits integrated into these quantum systems. 

Scientists have long used standard electrical transport measurements such as resistivity and the Hall effect to gain information on the electronic properties and structure of materials. Now quantum transport measurements can be used to study this and the fractional quantum Hall effect in two-dimensional electron gases and topological insulators inform researchers on material properties with quantum mechanical effects.

The ultra-low temperatures and high magnetic fields provided by Oxford Instruments dilution refrigerators and integrated magnets are key research tools for revealing quantum properties. Systems, such as the Oxford Instruments Triton, already lead the way in experiment-readiness with high-density RF and DC wiring capability, unique sample exchange mechanisms and superconducting magnet integration. SPECS Nanonis Tramea is a natural complementary partner to the Triton, with its fast, multi-channel, multi-functional capability; it forms a full replacement for the traditional measurement rack of disparate electronic measurement units.

 

*Dr Harriet van der Vliet’s work is related to new product development with an emphasis on quantum transport measurement systems. Previously, she worked in ultra-low temperature physics, cooling two dimensional electron gases into the milli Kelvin regime. Harriet is a member of the Institute of Physics, UK.