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Thursday, 11 April 2019

Schrödinger’s computer out of the box or the future of quantum computing

Although quantum computing is a growing field of research, as we know it today it presents serious limitations to become a practical way of computing. That was the controversial argument developed by Dr Xavier Waintal in an ICN2 Seminar held on 8 April. He claims that governments should invest in fundamental research rather than in very specific applications.

An ICN2 Seminar on quantum computing was held on 8 April. Hosted by ICREA Prof. Stephan Roche and ICREA Prof. Sergio Valenzuela, the speaker was Dr Xavier Waintal, a condensed matter theoretical physicist with research interests in quantum nanoelectronics, spintronics and strongly correlated systems. He develops his research at CEA Grenoble, France, and is the head of the Theoretical Physics Group of PHELIQS (Quantum Photonics, Electronics and Engineering Lab).

In his talk, entitled “A physicist introduction to quantum computing or quantum error correction as seen by a skeptic”, Waintal shared his doubts about the future of quantum computing. Although quantum computing holds the promise of an exponential speed up of certain tasks with respect to classical computers, serious difficulties arise when trying to get an actual quantum computer, according to the speaker.

One of them is related to the fact that a quantum computer is an analogue machine. This means that its internal state is described by continuous variables. With a relatively small number of qubits, you will need to perform interference experiments with unprecedented precision for measuring the angles involved.

Paradoxically, at the moment, the more qubits you have, the less operations you can do with your quantum computer. Using many qubits to get a so-called logical qubit aims to solve this issue. However, as the system gets more complex, new unpredictable errors appear. As Waintal emphasised, a serious limitation of quantum error correction codes is that “they only catch errors for which they have been designed.”

In summary, despite his apparent pessimism, Waintal agrees that remarkable progresses have been made in the field of quantum computing. Nevertheless, he stresses that governments should not primarily invest in very specific applications that could end up in a dead end, but in fundamental research to explore completely new ways to tackle these issues.