Hans Briegel on the Advances and Applications of Quantum Computers
Interview for the Special Topic of Quantum Computers, August 2010
Continuing with the theme of one-way quantum computation, you have two further papers with Robert Raussendorf as co-author. How did those papers take this field forward?
In "Measurement-based quantum computation on cluster states" (Phys. Rev. A 68: 2003), written together with Daniel E. Browne, who is now lecturer at University College London, we elaborated on many theoretical and practical details of the scheme of measurement-based quantum computation. This includes, for example, a compendium of explicit measurement patterns for certain quantum circuits, such as the quantum Fourier transform, or the quantum adder.
The idea of the paper was to provide a kind of "manual" for measurement-based quantum computation, for someone who would build such a device in the laboratory and then run an algorithm on it. In this paper, we also introduced the generalized notion of graph states, which has played an important role for some of my later research.
"Computational model underlying the one-way quantum computer" (Quant. Inf. Comp. 2: 443-86, 2002), explored other advantageous ways of information processing with the one-way computer, beyond the simulation of quantum logic circuits.
Another of your highly cited papers is the 2004 Nature paper with Zin Zhao as lead author, "Experimental demonstration of five-photon entanglement and open-destination teleportation" (430: 54-8). How did that collaboration come about? You describe a demanding experimental set-up for five-photon entanglement. What are the main findings of the paper?
When Jian Wei Pan (now at Hefei, China) visited me once in Munich, we talked about our investigations of cluster and graph states and I suggested that these states could also be used for multi-user quantum networks, allowing for flexible communication channels or for distributed quantum computation.
"We are trying to understand the implications of quantum mechanics for novel ways of information processing, both in man-made devices and in natural systems."
The simplest example was open-destination teleportation in which several users (Alice, Bob, Charlie...) participate. An unknown quantum state in the hands of Alice is first teleported into a joint state held or shared by the other users. Later, these users may decide who of them will retrieve Alice's state. Since the destination of the teleportation is not fixed at the beginning, we called it open-destination teleportation.
The theoretical idea was quite simple, different from the experiment, which I think was quite challenging at the time. Furthermore, the experiment also constituted the demonstration of an important property of graph states.
Have I overlooked anything in your highly cited papers?
I should mention a few related recent papers with Maarten Van den Nest, Akimasa Miyake, and Wolfgang Dür:
- Van den Nest M, et al., "Universal resources for measurement-based quantum computation," Phys. Rev. Lett. 97: 2006.
- Van den Nest M, et al., "Fundamentals of universality in one-way quantum computation," New J. Phys. 9: 2007.
- Van den Nest M, et al., "Classical simulation versus universality in measurement-based quantum computation," Phys. Rev. A 75: 2007.
In these, we addressed the questions: Where does the power of a quantum computer come from? How is it related to the entanglement of the resource state, and what is special about the cluster states? We showed that there exist indeed many other states that can be used as a universal resource, but for all of them their entanglement seems to be the essential property— the fuel, so to speak, of the quantum computer.
In these papers, we were also able to give concise mathematical conditions, in terms of entanglement, that any universal resource must fulfill, such as how fast its entanglement must at least grow with the number of particles. Our investigations were part of an increased effort to understand the basic structures of quantum computation.
Thank you, Hans, for those insights into why the papers we have been discussing are high impact. In conclusion, can you to tell me about the future trajectory of your research?
We have recently started (together with Sandu Popescu of the University of Bristol, UK) to explore quantum information processing capabilities of biological systems and systems that work at the borderline of nanophysics and molecular biology. These systems typically operate at room temperature and with high levels of noise. On the other hand they operate far away from thermal equilibrium, and we believe that this offers new capabilities for quantum information processing which have hitherto not been fully recognized.
Of course, this field is still in its infancy, and progress will require a closer interdisciplinary collaboration, but the question to what extent genuine quantum effects play a role in biology is of fundamental interest and exciting.
Professor Hans Briegel
Institut für Theoretische Physik
Universität Innsbruck
and
Institut für Quantenoptik und
Quanteninformation
Österreichische Akademie der Wissenschaften
Innsbruck, Austria
Hans Briegel MOST CURRENT MOST-CITED PAPER IN ESSENTIAL SCIENCE INDICATORS:
Raussendorf R, Briegel HJ, "A one-way quantum computer," Phys. Rev. Lett. 86(22): 5188-91, 28 May 2001, with 763 cites. Source: Essential Science Indicators from Clarivate.
KEYWORDS: QUANTUM COMPUTATION, INFORMATION PROCESSING, ATOMIC LEVEL, PUBLIC-KEY CRYPTOGRAPHIC SYSTEMS, COMPLEX QUANTUM SYSTEMS, QUANTUM MECHANICS, MAN-MADE DEVICES, NATURAL SYSTEMS, SIMULATION, COMPLEXITY, ENTANGLEMENT, OPTICAL LATTICE, CLUSTER STATES, ONE-WAY QUANTUM COMPUTER, MEASUREMENT, GRAPH STATES.
Citing URL: http://sciencewatch.com/ana/st/quantum/10augSTQuanBrie/