Reimagining the laser: new ideas from quantum theory could herald a revolution - The Conversation AU

A crucial difference between lasers and traditional sources of light is the “temporal coherence” of the light beam, or just coherence.

The coherence of a beam can be measured by a number C, which takes into account the fact light is both a wave and a particle.

The coherence C is roughly the number of photons (particles of light) emitted consecutively into the beam with the same phase (all waving together).

For example, in many quantum computers, we will need a highly coherent beam of light at a specific frequency to control a large number of qubits over a long period of time.

Future quantum computers may need light sources with even greater coherence.

They stated that the coherence C of the beam cannot be greater than the square of N, the number of energy-excitations inside the laser itself?

Basically, Schawlow and Townes made assumptions about how energy is added to the laser (gain) and how it is released to form the beam (loss).

We introduced a new model, which differs from a standard laser in both gain and loss processes, for which the coherence C is as big as N to the fourth power?

Moreover, we show a laser of this kind could in principle be built using the technology of superconducting qubits and circuits which is used in the currently most successful quantum computers.

It is important to note that, in both cases, the laser would not produce a beam of visible light, but rather microwaves.

No, at least not if the laser beam has the ideal coherence properties we expect from a laser beam

Coherence proportional to the fourth power of the number of photons is the best that quantum mechanics allows, and we believe it is physically achievable