Quantum 'Logic Gates' Could Advance Computing

Physicists have demonstrated that atom and light photons can be controlled to make a "logic gate." The system could be used to make super-fast computing devices.

The quantum logic gate system has combined two techniques; information processing using stationary atoms,and photons for quantum communication. A photon is a quantum particle of light.

The quantum logic gate was developed by researchers at Max Planck Institute of Quantum Optics in Garching.

All modern computers run on the idea of 'logic gate' developed by Gottfried Wilhelm Leibniz over 300 years ago. Leibniz showed that all information can be encoded into a binary system and can be decoded using logic gates. These logic gates follow the 'truth table' to generate output signals based on input data. Modern computers have several electronic circuits containing millions of these logic gates.

Quantum bits or quibits can exist in several states at once. The binary system of these quantum particles is represented by 1 "up" and 0 "down." For photons the polarization states are represented by left or right circular. Note that qubits can exist in both states and a superposition state simultaneously.

The logic gate in the current research consists of a single atom trapped in a "light cavity" made of two mirrors. Researchers could switch the state of the photon by reflecting it off the atom in the cavity, Nanowerk reported.

"In our experiment we measure both the polarization of the reflected photons and the spin orientation of the atom after the gate operation. At present, we achieve an efficiency of about 70%. By further improving the mirror parameters this value could be significantly improved", Andreas Reiserer, one of the study authors said in a news release.

The process can entangle the atom and photon.

In quantum physics, particles can remain connected in the same state, despite being far away from each other. Albert Einstein called the phenomenon of quantum entanglement as "spooky action at a distance." Research has shown that a beam of laser fired through a crystal can create pairs of entangled photons.

In the current study, Max Planck physicists were able to create an atom-photon couple. The team demonstrated that this hybrid atom-photon system can act as a classical logic gate. This entangled state of the qubits is essentially what makes a quantum computer different from regular computers.

The team conducted an experiment to see whether the system could use the logic gate to generate atom-photon couples from input atom and light quanta.

Researchers sent two laser pulses in the system and found that they could entangle an atom and two photons. The team then manipulated the atom in the second step and detangled the system, leaving a pair of coupled photons. 

"Quantum communication, using flying photons, and data processing with atoms or ions have been regarded as separate research fields so far," Prof. Gerhard Rempe, one of the study authors said. "In our experiment we merge both techniques. In particular, our quantum gate could be easily implemented in a network in which atoms serve as stationary nodes for the storage of information, whereas photons transmit the information between these nodes, even over large distances. In this way we hope to contribute to the realization of a scalable quantum computer."

The study is published in the journal Nature.

Another study by researchers at Massachusetts Institute of Technology has demonstrated an alternative method of quantum coupling. Researchers used laser to suspend a single atom of the metal rubidium in a lattice of light. The system could also generate entangled states that can be used in future computers.