Quantum technique transfers two photon properties
The bandwidth for quantum teleportation has doubled. A new technique transfers information about one particle so that another particle takes on two, rather than just one, of the original particle’s quantum properties.
Chinese researchers accomplished the feat by nesting one quantum teleportation apparatus inside another. “It’s impressive,” says Wolfgang Tittel, a quantum physicist at the University of Calgary in Canada. “It’s conceptually very simple but technically very difficult.”
The achievement, reported in the Feb. 26 Nature, does not bring scientists much closer to teleporting pens, puppies or people à la Star Trek. But teleporting multiple properties over large distances would enhance proposed quantum communication networks that rely on encoding information in particles’ delicate quantum properties.
The Chinese team, led by Jian-Wei Pan and Chao-Yang Lu of the University of Science and Technology of China in Hefei, largely stuck to the tried-and-true teleportation technique proposed in 1993. That method requires three particles (in this case, particles of light, or photons): one being teleported plus a pair of particles that are quantum entangled. Entanglement establishes a connection between particles so that physicists can measure a property of one photon and determine what the value of that property will be when the partner photon is measured.
The teleportation process begins with a measurement that compares a property, usually polarization, of the photon getting teleported with the same property of one of the entangled photons. That measurement destroys the quantum nature of both photons (and usually the photons themselves). But the information gleaned from the comparison enables physicists to manipulate the third photon so that its polarization perfectly matches that of the original photon.
Then the team added a few tricks. First, the researchers entangled the particle pair so that two properties — polarization plus orbital angular momentum (the “twistiness” of the photon’s trajectory) — were connected. Then the physicists found a way to determine polarization while preserving the measured photons and some of their quantum properties. Whenever the polarization sensor obtained a certain measurement, one photon got fed into equipment that teleported the photon’s orbital angular momentum to a new photon. One last detector then compared the orbital angular momentum of the new photon with that of the original entangled photon. By completing both rounds of measurements, the physicists proved that they could manipulate the final particle so that its polarization and orbital angular momentum perfectly matched those of the original photon.
Lu says that he and his team expect to be able to teleport three properties of a photon within a few years. Even if they succeed, there’s still a long way to go before physicists can completely reproduce particles in a new location. A photon would be the simplest particle to fully teleport, Tittel says, yet even it has several other properties such as frequency and direction of propagation that would have to be transmitted. Still, he says that teleporting two properties is a big upgrade over just one. Each property can be considered a quantum bit of information, he says, so teleporting more properties increases the amount of data that a single particle can carry.