A all-optic switch controlled by a single photon

Researchers develop a all-optic switch:

Electron, a subatomic elementary particle carrying a negative charge plays an important role in many physical phenomena like electricity, magnetism and thermal conductivity. When accelerated , absorbs or radiates energy as photons. In our everyday life we use devices operating on these current which is nothing but due to the flow of electrons. Thereby playing a vital role in all areas of electronics (the name is derived due to extensive requirement of electrons).In digital computer chips these electricity operated transistor act as switches.

But with the advent of optics, having several advantages over electricity has compelled scientists develop new techniques to use light for several applications. One popular being optical fiber for communication purpose, achieving higher transfer rates and less distortion.

Now the researchers have come up with a all-optic transistor that can replace fundamental component, transistor switches in classical and quantum computers marking the beginning of optical computing era. The Quantum computers use the power of atoms to perform memory and processing tasks.

This revolutionary all-optic transistor uses photons. The researchers at MIT's Research Laboratory of Electronics, Harvard University and Vienna University of Technology developed a all-optical switch in which the transmission of light is controlled by a single photon nothing but light and so is named as all-optic. 

The all-optic switch uses a pair of highly reflective mirrors placed opposite to each other forming an optical cavity. The dual nature of light that allows it to be a photon as well as a wave is necessary to understand the working. The ON state means that the beam of light can passes through both the mirrors while in OFF state around 20% of light is able to pass through both. suitable adjustment of inclination and distance between to wavelength of light, precisely so as to allow the light at particular frequency from source to pass through both the mirrors. The light while moving in a resonant cavity builds up large field in the cavity that is enough to cancel the field moving back after reflection, allowing only forward moving fields.

The cavity space is filled with a gas of supercooled cesium atoms which do not affect the motion of light passing through. Light continues in one direction passing both mirrors indicating ON state. The state remains as it is until a 'gate photon' is sent inside the cavity space which would excite an electron of a cesium atom to a higher state which is sufficient to change the way the whole cavity acts in response to light thereby being opaque, permitting very small amount of light to pass through giving an OFF state.

Enabling the existing of mutually exclusive states, called superposition is possible in case of all-optic switch since photon don't interact easily allowing parallel computation depicting all possible solutions. The quantum computers built with processors using this all-optic switch would be able to keep "qubits" or quantum bits which is hard to keep otherwise and even create quantum states.

Optic switch can be employed even for photo-detection since if a photon is present it would strike cesium atom exciting an electron creating a opaque path for light. 

The interesting advantage is that it can do the switching work at a single photon level requiring very less power for each bit since one bit is carried by only one photon.

But this design cannot be incorporated in chips due to use of supercooled cesium atoms and hence need an alternative design.

Thereby development of optics is creating way for faster, efficient and compact processors using less power and dissipating very little heat which would work solely on light which is a contrast and advantageous to existing which dissipates more heat and even needs more power. Only a fraction of power would be sufficient for it to work.