When the pigeon and the letter do not travel together

July 23, 2019

Whether it is pigeons in the air, electrons in a telegraph wire, radio waves from a cell phone or single photons in an optical fiber, in standard communication, there is always a particle or wave involved in the information exchange between two parties; say Alice and Bob. However, in quantum mechanics, one can send information from Alice to Bob while the particle or wave involved in this information exchange travels from Bob to Alice.

In an international collaboration led by Philip Walther, scientist from the University of Vienna teamed up with the University of Cambridge and the Massachusetts Institute of Technology to implement a new counterfactual communication protocol. In standard photonic communication, the information is encoded in single photons; thus, the information and the single photons travel in the same direction. However, in counterfactual communication there is no carrier found travelling in the same direction as the message. In this implementation, single photons would travel from Alice to Bob while information would travel from Bob to Alice.

What carries the message then? Even before receiving the single photon, Bob prepares his setup according to the information bit that he wants to send, either 0 or 1. In this way, he sends the single photon back if he wants to send a bit 1 or keeps the photon in his laboratory if he wishes to send a bit 0. Counterintuitively, the Zeno effect, which was first discovered by cryptanalyst Alan Turing, enables Bob to send the photon back without actually interacting with it. Alice will then interpret Bob's message by observing whether the sent photon is returned or not. Thus, the presence and the absence of single photons is enough to encode any message.

In previous counterfactual communication protocols, there remains some uncertainty as to whether Bob interacted with the photons or not. In this new implementation the two main drawbacks of earlier implementations, weak trace and postselection, have now been completely overcome. "In our implementation, there is no trace of the photon travelling in the same direction as the information and we are able to compensate the message errors without discarding information bits." says I. Alonso Calafell, one of the authors from the publication.

By combining an integrated photonic platform built at MIT, together with a novel theoretical proposal developed at the University of Cambridge, scientist from the University of Vienna contradicted a crucial premise of communication theory: that a message is always carried by physical particles or waves.
-end-
Publication in npj Quantum Information:

"Trace-free counterfactual communication with a nanophotonic processor" Irati Alonso Calafell, Teodor Strömberg, David Arvidsson-Shukur, Lee Rozema, Valeria Saggio, Chiara Greganti, Nicholas Harris, Mihika Prabhu, Jacques Carolan, Michael Hochberg, Tom Baehr-Jones, Dirk Εnglund, Crispin Barnes, and Philip Walther, npj Quantum Information, 23 July 2019.

DOI: 10.1038/S41534-019-0179-2

University of Vienna

Related Quantum Mechanics Articles from Brightsurf:

Theoreticians show which quantum systems are suitable for quantum simulations
A joint research group led by Prof. Jens Eisert of Freie Universit├Ąt Berlin and Helmholtz-Zentrum Berlin (HZB) has shown a way to simulate the quantum physical properties of complex solid state systems.

A new interpretation of quantum mechanics suggests reality does not depend on the measurer
For 100 years scientists have disagreed on how to interpret quantum mechanics.

New evidence for quantum fluctuations near a quantum critical point in a superconductor
A study has found evidence for quantum fluctuations near a quantum critical point in a superconductor.

Simulating quantum 'time travel' disproves butterfly effect in quantum realm
Using a quantum computer to simulate time travel, researchers have demonstrated that, in the quantum realm, there is no 'butterfly effect.' In the research, information--qubits, or quantum bits--'time travel' into the simulated past.

Orbital engineering of quantum confinement in high-Al-content AlGaN quantum well
Recently, professor Kang's group focus on the limitation of quantum confine band offset model, the hole states delocalization in high-Al-content AlGaN quantum well are understood in terms of orbital intercoupling.

A Metal-like Quantum Gas: A pathbreaking platform for quantum simulation
Coherent and ultrafast laser excitation creates an exotic matter phase with spatially overlapping electronic wave-functions under nanometric control in an artificial micro-crystal of ultracold atoms.

Fluid mechanics mystery solved
An environmental engineering professor has solved a decades-old mystery regarding the behavior of fluids, a field of study with widespread medical, industrial and environmental applications.

Quantum leap: Photon discovery is a major step toward at-scale quantum technologies
A team of physicists at the University of Bristol has developed the first integrated photon source with the potential to deliver large-scale quantum photonics.

USTC realizes the first quantum-entangling-measurements-enhanced quantum orienteering
Researchers enhanced the performance of quantum orienteering with entangling measurements via photonic quantum walks.

A convex-optimization-based quantum process tomography method for reconstructing quantum channels
Researchers from SJTU have developed a convex-optimization-based quantum process tomography method for reconstructing quantum channels, and have shown the validity to seawater channels and general channels, enabling a more precise and robust estimation of the elements of the process matrix with less demands on preliminary resources.

Read More: Quantum Mechanics News and Quantum Mechanics Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.