Turn rubium atoms into a single photon server

Each time you turn on a light bulb, there is the energy of 10 to 15 visible photons, the fundamental particles of light, that will illuminate the room every second. If it is too bright for you, light a candle. If that's too bright and that you only need one and no more than one photon each time you turn on the switch, you'll have to work a little harder.

A group of physicists in Professor Gerhard Rempe's group at Max Planck Quantum Optics Institute in Garching near Munich (Germany) has built a single photon server, based on a single neutral atom that is trapped. The high quality of these single photon particles and their availability are important for future quantum information processing experiments with single photons. In the relatively new field of quantum information processing, the goal is to utilize quantum machines to be able to calculate certain tasks that are far more efficient than a classical computer.

A single atom, due to its nature, can only release one photon at a time. A single photon particle can be created arbitrarily by applying a laser pulse to a trapped atom. By placing a single atom between two highly reflective mirrors, called niches, all these photons will be emitted in the same direction.

Compared to other single-photon generation methods, these photons are of very high quality, meaning there is little energy variation and they can be controlled. For example, it can make them homogeneous, a very necessary property for quantum calculations. On the other hand, until now, it is not possible to trap a neutral atom in a cavity and at the same time create single photons in a time long enough to be able to use these photons in a practical way.

A single atom is trapped in a cavity that produces a single photon after being activated by a laser pulse.(Photo: Max Planck Quantum Optical Institute)

In 2005, Professor Rempe's team increased the number of traps of atomic units in a cavity significantly by using three-dimensional recessive cooling methods. In this article, they publish the results that they were able to combine this cavity cooling method with the creation of single photons in such a way that a single atom could release 300,000 photons.

In their current system, the time that an atom is available is much longer than the time it takes to cool and trap the atom. Because this system can operate with a large load cycle, the distribution of photons to users is possible. This system acts as a single photon server.

This experiment uses a magneto optical trap to create rubidium atoms in a vacuum chamber. These atoms are then trapped inside the cavity in the dipole potential of the focused laser. By applying a series of laser pulses from the side, a single stream of photons will be emitted from the cavity. Between each release of a single photon, the atom is cooled to prevent it from moving away from the trap.

To prove that no more than one photon is produced after each laser pulse, the photon stream is directed at the beam splitter, which directs 50% of the photon into a detector and the remaining 50% into the second detector.

A single photon will be detected either by detector 1 or by detector 2. If two detectors match, there must be more than one photon present in the laser pulse. Thus, if there is no overlap, then it proves that, only one and no more than one photon is produced at the same time, one thing is very convincing in this study.

With the current progress, the quantum information processing with photons has come a step closer. By operating a single photon server, Professor Gerhard Rempe and his team are ready to take on the next challenges such as atomic-photon experiments that determine determinism and experiments that connect atoms - integers. atom-atom entanglement.

Thanh Van