Posted in: IBM Research-Zurich, Nanotechnology, Quantum Computing, Uncategorized

Quantum Transport Goes Ballistic

IBM scientist Johannes Gooth is focused on nanoscale electronics and quantum physics.

Published today in the peer-reviewed journal Nano Letters, IBM scientists have shot an electron through an III-V semiconductor nanowire integrated on silicon for the first time. This achievement will form the basis for sophisticated quantum wire devices for future integrated circuits used in advanced powerful computational systems.

IBM scientist and lead author on the paper Dr. Johannes Gooth explains the paper in this Q&A.

The title of your paper is Ballistic one-dimensional InAs nanowire cross-junction interconnects. When I read “ballistic” rather large missiles come to mind, but here you are doing this at the nanoscale. Can you talk about the challenges this presents?

Johannes Gooth (JG): Yes, this is very similar, but of course at a much different scale. Electrons are fired from one contact electrode and fly through the nanowire without being scattered until they hit the opposed electrode. The nanowire acts as a perfect guide for electrons, such that the full quantum information of this electron  (energy, momentum, spin) can be transferred without losses.

We can now do this in cross-junctions, which allows us to build up electron pipe networks, where quantum information can perfectly be transmitted. The challenge is to fabricate a geometrically very well defined material with no scatterers inside on the nano scale. The template-assisted selective epitaxy or TASE process, which was developed here at the IBM Zurich Lab by my colleagues, makes this possible for the first time.

How does this research compare to other activities underway elsewhere?

JG: Most importantly, compared to optical and superconducting quantum applications the technique is scalable and compatible with standard electronics and CMOS processes.

What role do you see for quantum transport as we look to build a universal quantum computer?

JG: I see quantum transport as an essential piece. If you want to exercise the full power of quantum information technology, you need to connect everything ballistic: a quantum system that is fully ballistically (quantum) connected has an exponentially larger computational state space compared to classically connected systems.

Also, as stated above, the electronics are scalable. Moreover, combining our nanowire structures with superconductors allows for topological protected quantum computing, which enables fault tolerant computation. These are major advantages compared to other techniques.

How easily can this be manufactured using existing processes and what’s the next step?

JG: This is a major advantage of our technique because our devices are fully integrated into existing CMOS processes and technology.

What’s next for your research?

JG: The next steps will be the functionalization of the crosses, by means of attaching electronic quantum computational parts. We will start to build superconducting/nanowire hybrid devices for Majorana braiding, and attach quantum dots.

Universal quantum computer here we come.

Ballistic one-dimensional InAs nanowire cross-junction interconnects, Johannes Gooth, Mattias Borg, Heinz Schmid, Vanessa Schaller, Stephan Wirths, Kirsten E Moselund, Mathieu Luisier, Siegfried Karg, and Heike Riel, Nano Letters, DOI:10.1021/acs.nanolett.7b00400, Publication Date (Web): March 23, 2017




  1. Muir Kumph says:

    This looks like promising research. However, I don’t know why JG says that optical and superconducting applications are not scalable compared to this research. IBM is building superconducting based quantum computers: see . How far they scale, is an open question. But there are no known fundamental reasons to stop it from being scaled up.

    1. Johannes Gooth says:

      The limit is the down scaling of the single qubit size. Microwave technology requires microwave sized components. The quantum wire qubits can, in principle, be scaled down to the nanoscale. Of course you may ask whether a high packing density like in conventional computers is required at all, because you generate essentially an exponentially larger computational state space in quantum computers, compared to the classical linear case. This is a valid question, which answer we might get in the future.

      At this time, one thing is very important: To date, superconducting qubits work and can be operated. Nanowire qubit operation, so far, has not been demonstrated and I think there is still have a long long way to go. But if they come, the TASE process, developed by IBM, provides an ideal technology platform to put us in the lead.

      1. Muir Kumph says:

        Actually, superconducting qubits can be much smaller than the wavelength of microwave radiation; even nanoscale. Maybe you are thinking of the microwave resonators used for some devices. The resonators are part of some superconducting quantum computing architectures, but not all. So I would say that IBM’s superconducting qubits are actually quite scalable.

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Johannes Gooth

"If you want to exercise the full power of quantum information technology, you need to connect everything ballistic."