Last week, the Royal Swedish Academy of Sciences awarded the 2012 Nobel Prize in Physics to Serge Haroche, of the Collège de France and Ecole Normale Supérieure in Paris, France, and David Wineland, from the National Institute of Standards and Technology and the University of Colorado Boulder, US. Both researchers used independent yet complementary methods to advance the field of quantum optics, which is the study of fundamental interactions between light and matter. Their work is a significant step in making the dream of quantum computers a reality.

### Clarifying Schrödinger's cat paradox

The Nobel Laureates practically tested Erwin Schrödinger's 1935 thought experiment of a cat in a box, which also contains deadly cyanide. The idea is that the cyanide is released only after the decay of a radioactive atom governed by the laws of quantum mechanics. This theory explains the crazily counter-intuitive interactions between the quantum world and the classical physics world we see and here.

In a quantum system, particles or atoms can exist in two states simultaneously - a superposition. Therefore, the radioactive material has decayed and not decayed. And Schrödinger's cat is both dead and alive - peeking inside the box risks killing the cat because the quantum superposition of the radioactive material is so sensitive to exchanges with the outside environment.

Haroche and Wineland verified how the act of measuring causes a quantum state to collapse and lose its fragile superposition. Haroche and his team controlled and measured trapped photons inside a vacuum cavity, as well as sending Rydberg atoms through the cavity. According to the Royal Swedish Academy of Science's scientific background report that summarizes the work of both physicists, the researchers essentially made a movie of how photons evolve from a superposition to a classical state.

David Wineland and his colleagues took the opposite approach, trapping electrically charged ions and using laser pulses - photons - to put the ions in their lowest energy state, and measured their quantum properties.

For both researchers, keeping their particles at temperatures near absolute zero (−273.15 °C or −459.67 °F) was key to controling and measuring them.

### When will the quantum computing revolution come?

Wineland and his group experimentally carried out the first two-qubit operation with beryllium (Be+) ions. Qubits are basic units of information that can be a 0 or 1 simultaneously, unlike classical bits which can only store data as either 0 or 1. In theory, a quantum computer of 300 qubits could hold two to the power of 300 values simultaneously, which is more than the number of atoms in the known universe. This tiny computer could perform an incredible amount of calculations simultaneously.

Today's most advanced quantum computer technology has been demonstrated with up to 14 qubits, and a series of gates and protocols. The next - and most challenging - step towards making a quantum computer is solving the conundrum of ensuring qubits are sufficiently isolated from their environment so as not to affect their quantum properties, while still being able to communicate their calculations to the outside world.

*- Adrian Giordani*