Sunlight, comprised of beams of photons, streams through blue water. Now French physicists claim to have created a device that traps photons for a seventh of a second.
Credit: iStockphoto
PARIS: In 1927, Albert Einstein conceived of a box in which light was trapped and a single light particle, or photon, was released in a theoretical experiment to measure the relationship between mass and energy.
Eighty years on, French physicists say they have actually created Einstein's box: a device just 2.7 cm2 that snares a photon, enabling it to be monitored from birth to death.
Photons are arguably the ultimate existential particle in physics. By switching on a light bulb, you release a million billion photons every second. But as soon as you see a photon, it dies, for its contact with the retina expends the energy that made it exist.
"Photons are easy to detect. You do it yourself, every second for instance when you are looking at a computer screen," said study author Jean-Michel Raimond of France's National Centre for Scientific Research (CNRS). "But you do this only once. It's post-mortem analysis. [Now] we can analyse it in real time, while the photon is still alive."
The box comprises a cavity with walls made from ultra-reflective, superconducting mirrors able to trap a photon for about a seventh of a second.
That may not seem much but it is worth considering that, in the same time, a free photon would travel about a tenth of the distance from the Earth to the Moon.
The conventional way of counting photons is by a light detector which works by absorbing the energy by impacting particles. But the collision destroys the photons; what researchers really needed was a "transparent" counter.
The French team, who report their work in the British journal Nature today, say they found their counter in the form of a stream of rubidium atoms, which cross the box in which the photon is trapped.
Photons have an electrical field that slightly changes the energy levels of the atom, but in this case, not enough to let the atom absorb energy from the field.
When an atom crosses the photon's electrical field, this causes a tiny delay in the electrons that orbit the atom's nucleus. The delay is measurable, using the same technique as modern atomic clocks, which use electrons' orbit as a "pendulum" to provide a precise time.
The findings come in the wake of other extraordinary advances in the study of light this year. In February, physicists from Harvard University reported that, taking advantage of an untested quirk of quantum mechanics, they had managed to slow photons down to a standstill and then cause them to 'jump' through space (see A trick of the light, Cosmos Online).
The new findings, though, could have immediate application in the real world. In a commentary published in Nature along with the study, Ferdinand Schmidt-Kaler, a quantum physicist at Germany's University of Ulm, described the French achievement as an "experimental masterwork" with major implications for quantum computing, a field that proponents claim will make today's supercomputers look like an abacus.
Instead of using the binary digits 0 and 1 to hold information, quantum computing is based on another mind-bending principle of quantum mechanics - changes of state, called superposition, that occur at atomic level.
Quantum information, or a qubit, can be a 0 or 1 or simultaneously as both 0 and 1, amounting to a fanastic potential boost in data storage, but only useful so long as it can be controlled and accessed.
Photons, atoms and ions have been used as qubit carriers in this still fledgling area of research. The experiment demonstrates that "a stream of atomic qubits can be fully controlled by the qubit state of a trapped photon," said Schmidt-Kaler.
A related article that I would like the author to take note of
The following article was in MSN news at the link:
http://news.in.msn.com/national/article.aspx?cp=documentid=1143065
I would like to bring to notice the editor of the cosmos magazine and the author of this artice that the following discovery, coupled with what the above article is about could be a milestone for science. Should not be ignored.
Indian physicists trap light in 'nano' soup
Bangalore: Indian scientists have demonstrated how to trap and retrieve light using a soup of micro and nano sized magnetic spheres — a major milestone in the path towards developing optical computers.
The researchers claim that their unique mixture of tiny particles works at room temperature, holds photons — the particles of light — for far longer than other systems, and can also be tuned with a magnet to store any wavelength of visible light.
The discovery made by a team led by Rasbindu Mehta at Bhavnagar University in Gujarat was first announced in the November issue of the Current Science journal published by the Indian Academy of Science in Bangalore.
Now, a report published in the latest issue of the Royal Chemical Society of London's journal Chemistry World says the discovery could pave the way for photonic 'microchips' that use photons for processing optical information in the same way electrons are manipulated in silicon chips in today's electronic devices and computers.
For over a decade, scientists have been working towards light-based computing that could be many times faster than electronics as light travels at a speed of approximately 300,000 km per second.
Any microchip designed to process optical signals has to store photons, perhaps by slowing or trapping light in carefully designed crystals. Mehta's team coated micron-size magnetite spheres with oleic acid and dispersed them through a ferrofluid, which is a suspension of much smaller magnetic nanoparticles.
When an external magnetic field was applied to the fluid, which was held in a glass cell, laser light passing through the medium was trapped inside. Photons escaped when the field was switched off.
"It is fantastic," said Hema Ramachandran, who heads the photonics unit at the Raman Research Institute in Bangalore, and was one of several physicists who witnessed the demonstration.
"It was a chance discovery," said Mehta's colleague Rajesh Patel.
While investigating the optical properties of their transparent fluid, the researchers noticed that in a certain magnetic field range, light scattering — both forward and backward — became zero.
"We thought the light got trapped inside," said Patel. "So, we switched off the laser (which was shining light through the system) and then the magnetic field, and there it was — a flash of colour lighting up our dark room."
Mehta said his group is yet to develop a theory to explain this novel phenomenon. He believes that the spheres are aligned by the magnetic field and form micro cavities — filled by the ferrofluid — in which the photons get trapped, resonating back and forth.
Changing the external magnetic field alters the refractive index of the cavities that in turn decides which wavelength of light is trapped by the system.
And what is more, according to Mehta, photons can be stored for as long as the magnetic field is switched on.
"This is the first visual evidence of storage and retrieval of light for a long and controllable duration. In all other reports, storage time of photons is restricted to a few nanoseconds," he said
Experiments by physicists in the US have involved stopping light altogether by using a gas of sodium or rubidium atoms chilled to near absolute zero, though that system is too complex and not practical for microchips.
Although Mehta's team seems to have chanced on a method for taming light that is simple, inexpensive and unsophisticated, its practical application is still years away.
photons
To an electromagnetic field, the magnetic field aspect, with respect to itself and respect to identical energy fields, behaves as a solid. It is the wave tension and ridigity and the long lost backaction of the Huygens' Principle that is the key to understanding the advancement of quantum teleportation, gravity and instant messaging independent of distance. C. Michael Turner