Posted: January 22, 2010

Quantum information processing - lifting the big veil

(Nanowerk News) The QIP (International Workshop on Quantum Information Processing) is a major meeting point for "quantum theorists". Renato Renner, an assistant professor of theoretical physics at ETH Zurich and co-organizer of this year's convention, explains why we will be contemplating application programs over the next few days even though we are still a far cry from a universally operational quantum computer.
Mr. Renner, how come scientists from all over the world are discussing which application programs could operate on a quantum computer when no such computer even exists yet?
It’s not all that different from the development of the conventional computer during the last century: on the one hand, you had people who were trying to build a computer whilst others were asking themselves what you could do with the computer once it existed. These were the people who concentrated on developing software. Today, you have the same divide: experimental physicists are trying to construct a quantum computer in a similar vein to the earlier vacuum tube and transistor computers whilst theoretical physicists and computer scientists are busy with the question as to what you can actually do with a quantum computer. The QIP is effectively the computer scientist conference of the future where we discuss the issue of how we can use these new information technologies. I consider this to be just as important a task because we wouldn’t be able to make good use of a quantum computer at this stage even if it did already exist.
What applications do the researchers have in mind?
To date, practically the only known application was the factorization of data, which could be used to crack cryptographic ciphering systems. Now, the primary aim is to simulate complex physical systems like a solid body. These systems are well understood in detail, but cannot be simulated using a conventional computer as they exceed its capacity. The quantum computer could accomplish this step.
What drives the scientists who take part in the QIP?
The key question is which applications – if at all – there are for a quantum computer beyond the scope of what a traditional computer can do. New ideas have recently emerged in this respect and considerable progress has been made.
What are their prospects?
Algorithms have been developed, for instance, that – unlike the conventional computer – can solve equations without even having to read the whole system of equation. Instead, the algorithms only have recourse to individual, relevant components of the system of equation.
Peter Shor is one of the “star speakers”. He is regarded as the driving force behind the construction of the quantum computer because he developed quantum algorithms for codes that can correct errors.
Yes, Shor demonstrated theoretically that you can correct hardware errors in calculations with a quantum computer. On a hardware level, errors – like in classical data processing – can never be avoided completely. In the case of the conventional computer, where there is only the conditions 0 or 1, the error correction is relatively simple. In quantum computers, however, there is an infinite number of intermediate conditions. Without correcting these errors, there would be little point in building a quantum computer.
What is he going to talk about?
He will be talking about so-called interactive evidence. This includes evidence regarding theorems which we know to be correct but which cannot be proved on paper. The theorem’s correctness can, to a certain extent, only be proved through the exchange of qubits between the party introducing the evidence and the one reviewing it.
What does that mean?
It raises profound questions: what statements can actually be proved? The surprising thing here is that the integration of quantum physics as an information technology tool changes the answer to this question. Statements that cannot be proved in a purely conventional world become provable. This is a recurring experience within quantum theory: suddenly things become possible that were deemed impossible in the conventional world. The previous purely classic view was therefore restrictive. We had a kind of veil over our eyes as we did not consider the possibility that the proof of a mathematical theorem could also be represented as a state of a quantum system.
What are the main themes of the convention?
The classic question in our field is how quantum physics can be used to process information. Recently, however, the question has also been the other way round, i.e. whether and to what extent information theory is useful in physics. These considerations are far-reaching. You could even conceive that the whole structure of quantum mechanics can be derived from basic assumptions regarding the behavior of information. One such assumption might be that information cannot move faster than light, or that information generally cannot be copied without it being altered in some way.
Where did the idea come from?
We noticed that computers developed from the classical view of physics were less efficient than when quantum physics was included. This raised the question as to what the concept of computing or information says about physics. Since the beginning of the new millennium, there have been initial results for this approach and now, for the first time, a complete session during the QIP. At the QIP, the initial approaches as to how interesting physical statements can be derived from information-theoretical axioms are presented. It also addresses the issue as to which “language” physical laws should be formulated in and whether the language of information theory is suitable. If so, that would mean a volte-face in our thinking as to how to approach physical issues.
How long has the workshop existed?
This is the 13th. It isn’t really a workshop any more, though, but rather a conference. The research field has grown tremendously since the first workshop. In the early days, 20 to 30 people would meet to exchange ideas; this year, over 300 scientists from all over the world are taking part. Because the field is still in its infancy, many issues have not yet been defined and the development is very open. Consequently, the discipline is also attracting many good students. The whole thing is proving to be highly successful.
What kinds of scientists convene there?
Physicians, mathematicians, electrical engineers and computer scientists, whose average age is very low. The fathers of this branch of research are between 50 and 60 years of age and the majority of the researchers in the field are under 40. This has an impact on conference proceedings, which are far less structured than in the case of long-established scientific disciplines and sometimes involve highly original events. Like spontaneous after-dinner talks and a show.
How will the conference open?
With a talk by a computer scientist on quantum computing from the perspective of computer science. Computer scientists previously found themselves in a special situation in that they assumed they could use a computer to simulate any other one. However, it is highly unlikely that a conventional computer can simulate the quantum computer efficiently. In this case a quantum computer would be useless as it couldn’t do any more than its conventional counterpart. The previous focus on purely classical information processing also resulted in some false conclusions. For instance, evidence that an absolutely secure encryption was impossible was established in classical information theory. However, we now have this through quantum cryptography.
Another prominent speaker will be Gilles Brassard, who invented quantum cryptography. Is this already used today without quantum computers or is it also merely a theoretical construct?
There is already a company in Switzerland that sells quantum cryptography. The box, which looks like a conventional computer, uses quantum information processing to produce encryptions. It reached market maturity in the last five years.
What will the first “real” quantum computer look like? Will it be kept at temperatures close to absolute zero to make it superconductive and thus minimize its susceptibility to errors?
Superconductivity is extremely useful but it remains unclear as to whether that will be the prevailing technology. There are ideas for technologies based almost exclusively on optics which do not necessarily require so much cooling, for example.
So it won’t need a special location like the LHC at CERN?
No, I believe the quantum computer can only be successful if we find a way to miniaturize it. The hope is that a similar breakthrough to the conventional computer will come, i.e. from the room-filling vacuum tube computer to the microchip.
When will the first quantum computer be put into service?
The question is what we really want to achieve. We already have the first product – quantum cryptography. The next step will be a quantum computer with a unique program that simulates a very special physical system - like a solid body. We can expect to see this over the next decade. Only then comes the fully equipped, freely programmable “universal quantum computer”. I doubt that this will happen in the next twenty years, though.
Source: ETH Life