Physics Nobel prize for quantum computing


Guess many of the professional bloggers have already posted about the very recent announcement on the Nobel prize in physics by the Royal Swedish Academy. Serge Haroche of Collège de France and École Normale Supérieure, Paris and David J. Wineland of NIST, Boulder, Colorado have been awarded the prize “for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems”.

First of all we can see that all the predictions failed this time (see my previous post). And I must admit I knew one of the winners, who is Prof. Haroche. I delivered a talk on circuit quantum electrodynamics (cQED) in IISc in the month of July.

In brief, cQED is a novel technology to tune quantum states by using electrical circuits which let photons to interact with atomic/electronic quantum states (hence QED) inside a resonator, which reflects the photons to bounce back-and-forth. Prior to the cQED, Haroche invented a technique, which is known as the cavity quantum electrodynamics (cavity-QED). In the cavity-QED a Rydberg atom (hydrogen like atom with large principal quantum number) is placed inside a cavity. The atom goes to a lower quantum state by emitting a photon. A microwave photon beam is also send inside the cavity through a small hole. The photons get reflected by the oppositely faced mirrors inside the cavity and during their back-and-forth motion they interact with the two states (higher and lower energy) of the atom. Thus the states inside the cavity remain as a superposition of two states or in a the Schroedinger cat state. Such a state forms the a qubit, which is the building block of a quantum computer.
[Interested readers can look at the 1989 Physics Today article by Serge Haroche and Daniel Kleppner and for a technical detail, the 2001 Review of Modern Physics issue by J. M. Raimond, M. Brune, and S. Haroche.]

Now for the other winner’s contribution, since I was not familiar with his name beforehand, I’ll speak a little. The video below shows David Wineland’s description of a quantum clock.

An atomic clock works on the principle of Rabi oscillation (physicist reader can take a look at the chapter 5 of J. J. Sakurai’s Modern Quantum Mechanics book), which is due to the oscillatory nature of the atomic states: an atom goes to a lower energy state by emitting light and again it comes back to the original higher energy state by absorbing the photon of the same energy (this happens in the cavity-QED as well). Instead of atoms, Wineland trapped Hg+ and Al+ by using electric field and let them interact with a visible wavelength laser with a narrow linewidth. In this way they achieved the optical clock, which has 100 times more accurate precision compared to the standard Caesium atomic clock (works in a microwave range).

Now people are saying that the Nobel prize has gone to the hands of the trappers: one has trapped photons, the other has trapped ions.

Useful references:
Article from the nobelprize.org
An article by Wineland group

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