Information transmitted between two particles instead of standard three
Quantum teleportation just got simpler and more reliable. The enhanced technique could lead to secure quantum networks for communication and computing.
Despite its sci-fi connotation, quantum teleportation doesn’t magically move objects but instead transmits fragile information. Unlike classical data — the 1s and 0s used in electronics — quantum information can exist in multiple states at once, as long as the particles encoding the data are not disturbed or measured. Teleportation allows for the transfer of a particle’s quantum state from one particle to another.
The standard procedure for quantum teleportation, proposed in 1993, requires three particles in all: the particle to be teleported, dubbed C, plus a pair of particles, A and B, that are entangled, meaning that they are linked in a way that measuring a property of one instantly reveals the value of that property for the other. The sender measures the desired property of particles A and C, thus ruining their quantum states. The sender calls up the receiver (or e-mails or faxes — any traditional method of communication will do) and shares the measurements. Based on that information, the receiver can modify particle B so that the desired property perfectly matches that of C before it was measured. In effect, B becomes C.
Using this method, scientists have teleported particles up to 143 kilometers (SN: 6/30/12, p. 10), but physicists including Ebrahim Karimi of the University of Ottawa had reservations. The sender’s simultaneous measurement of two photons requires expensive and complicated equipment. And even with those instruments, teleportation often fails. So Karimi and his colleagues designed an experiment that uses less sophisticated equipment and would theoretically transfer quantum information with 100 percent success. The method still requires a phone call; faster-than-light transmissions aren’t allowed.
Karimi’s demonstration used two photons. The researchers entangled the particles using a property called orbital angular momentum, a measure of how much a particle orbits around the axis of its forward motion. Under the 1993 scheme, the researchers would then have introduced a third particle and teleported its orbital angular momentum state. Instead, Karimi’s team encoded quantum information into a second property – polarization – of the sender’s entangled photon, A. The sender then measured both properties of the particle and sent the results to the receiver. The researchers could teleport the quantum information held in the polarization of A to the orbital angular momentum of B more than 99 percent of the time, they report in a paper posted April 30 at arXiv.org.
“By not using the third particle, the receiver always gets the right information,” Karimi says. “It’s a beautiful experiment,” adds Seth Lloyd, a mechanical engineer at MIT. “They’re actually doing teleportation in unconditional fashion – no ifs, ands or buts.”
Lloyd adds that the technique has potential for applications such as quantum cryptography and communication, as well as in linking future quantum computers. The teleported information is secure because an eavesdropper would need to intercept both the receiver’s entangled photon and the message reporting the sender’s measurements.
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