"We show that an optical frequency comb can be generated at single photon level,” says Zhenda Xie, associate professor and research scientist at UCLA. "Essentially, we’re leveraging wavelength division multiplexing concepts at the quantum level."
"Our goal is to advance quantum hyperentanglement for high-speed, unbreakable, secure communications," says Chee Wei Wong, Sc.D., associate professor of electrical engineering. "This is an enhancement package to dramatically speed up the current Quantum Key Distribution (QKD) rate, so our breakthrough leverages on the current QKD technologies, some of which are already implemented and released."
Wong explains that this technology is currently only relevant for transmitting medical databases, finance trading and banking information, government database communications and military communications in the field and war theatre. In other words, UCLA's quantum hyperentanglement research is just for communications, not for protecting data files and records at the source, like all those databases that were recently breached.
"The next step for us," says Wong, "is to demonstrate even more quantum bits encoded in the hyperentanglement approach. Currently, each photon carries about five quantum bits, at about 2^5 = 32 (2 to the 5th power), which is 32 times higher than the current unbreakable data rates. As the next step, we would also like to see information encoding on our physical system. Yes, in the absence of a quantum computer, this quantum physics-based communication approach is known to be unbreakable."
A research team at the University of Rochester is working with Duke University and the University of Glasgow on another new technique. This one uses twisted light to enhance the data capacity of each photon. The current process uses one of the four polarization orientations (e.g., horizontal, vertical, diagonal and anti-diagonal), which yields only one qubit per photon.
University of Rochester PhD student Mohammad Mirhosseini and colleagues used the orbital angular momentum (OAM) of light and the azimuthal angular position (ANG) of photons to encode the qubits, which doubled the capacity to 2.05. Basically, light has energy defined by its frequency and momentum defined by its wavelength. The orbital angular momentum is the wavefront of a beam of light that's coiling around its propagation axis. The electric field spirals around like a corkscrew; hence, twisted light. The quantum number describes how sharp the spiral is, while the sign reveals the direction of the spiral.
Using the "twisted light" technology, the team encoded a seven-dimensional alphabet and confirmed that the new system can generate and detect information at 4 kHz speeds with 93 percent accuracy. According to Mirhosseini, future plans include enhancing the transmission rates to GHz levels for communications/telecom applications and to extend the encoding to 4.17 bits per photon.
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