Researchers at the National Institute of Standards and Technology (NIST) have “teleported” (transferred) quantum information carried in photons over 100 kilometers (km) of optical fiber — four times farther than the previous record.

The experiment confirmed that quantum communication is feasible over long distances in fiber, according to the researchers. Other research groups have teleported quantum information over longer distances in free space (wirelessly), but fiber-optic cables offer more options for network design, the NIST researchers note.

Teleportation is useful in both quantum communications and quantum computing, which allow advancements in unbreakable encryption and code-breaking, respectively.

The new record, described in an open-access paper in Optica, involved the transfer of quantum information from one photon (its specific time slot in a sequence) to another photon* over 102 km of spooled fiber in a NIST laboratory in Colorado.

The achievement was made possible by NIST’s advanced single-photon detectors.

“Only about 1 percent of photons make it all the way through 100 km of fiber,” NIST’s Marty Stevens says. “We never could have done this experiment without these new detectors, which can measure this incredibly weak signal.”

Quantum internet

The new NTT/NIST teleportation technique could be used to make devices called quantum repeaters that could resend data periodically, extending network reach, perhaps enough to eventually build a “quantum internet.”

Previously, researchers thought quantum repeaters might need to rely on atoms or other matter, instead of light, a difficult engineering challenge that would also slow down transmission.*

* Various quantum states can be used to carry information; the NTT/NIST experiment used quantum states that indicate when in a sequence of time slots a single photon arrives. That teleportation method is novel in that four of NIST’s photon detectors were positioned to filter out specific quantum states. (See graphic for an overview of how the teleportation process works.) The detectors rely on superconducting nanowires made of molybdenum silicide. They can record more than 80 percent of arriving photons, revealing whether they are in the same or different time slots each just 1 nanosecond long. The experiments were performed at wavelengths commonly used in telecommunications.

Because the experiment filtered out and focused on a limited combination of quantum states, teleportation could be successful in only 25 percent of the transmissions at best. Thanks to the efficient detectors, researchers successfully teleported the desired quantum state in 83 percent of the maximum possible successful transmissions, on average. All experimental runs with different starting properties exceeded the mathematically significant 66.7 percent threshold for proving the quantum nature of the teleportation process.

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Abstract of Quantum teleportation over 100  km of fiber using highly efficient superconducting nanowire single-photon detectors

Quantum teleportation is an essential quantum operation by which we can transfer an unknown quantum state to a remote location with the help of quantum entanglement and classical communication. Since the first experimental demonstrations using photonic qubits and continuous variables, the distance of photonic quantum teleportation over free-space channels has continued to increase and has reached >100  km. On the other hand, quantum teleportation over optical fiber has been challenging, mainly because the multifold photon detection that inevitably accompanies quantum teleportation experiments has been very inefficient due to the relatively low detection efficiencies of typical telecom-band single-photon detectors. Here, we report on quantum teleportation over optical fiber using four high-detection-efficiency superconducting nanowire single-photon detectors (SNSPDs). These SNSPDs make it possible to perform highly efficient multifold photon measurements, allowing us to confirm that the quantum states of input photons were successfully teleported over 100 km of fiber with an average fidelity of 83.7±2.0%.