Chip-based devices improve practicality of quantum-secured communication

Science Daily  March 19, 2020 A team of researchers in the UK present secure key exchange up to 200 km while removing all side-channels from the measurement system. They used mass-manufacturable, monolithically integrated transmitters that represent an accessible, quantum-ready communication platform. This work demonstrates a network topology that allows secure equipment sharing which is accessible with a cost-effective transmitter, significantly reducing the barrier for widespread uptake of quantum-secured communication…read more. Open Access TECHNICAL ARTICLE

Quantum memories entangled over 50-kilometer cable

Phys.org  February 13, 2020 Researchers in China have demonstrated entanglement of two atomic ensembles in one laboratory via photon transmission through city-scale optical fibres. The atomic ensembles function as quantum memories that store quantum states. They used cavity enhancement to efficiently create atom–photon entanglement and quantum frequency conversion to shift the atomic wavelength to telecommunications wavelengths. They realized entanglement over 22 kilometres of field-deployed fibres via two-photon interference and entanglement over 50 kilometres of coiled fibres via single-photon interference. The experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the […]

Extending Quantum Entanglement Across Town

IEEE Spectrum  February 4, 2020 In an experiment researchers in Germany transferred the information contained in a single quantum bit from an atomic state to a single photon, then sent it through some 20 kilometers of fiber optic cable. They generated and observed the entanglement between a rubidium atom and a photon whose wavelength was transformed from 780 nm to the telecom S band at 1522 nm. The researchers found they can preserve on average some 78 percent of the entanglement between the rubidium atom and the fiber optic photon. Their next steps are to build out the full atom-to-photon-to-atom […]

A new twist on quantum communication in fiber

Phys.org  January 24, 2020 While Hilbert spaces with higher dimensionality it requires custom multimode fiber and limited by decoherence-induced mode coupling. An international team of researchers (China, South Africa) circumvented this by transporting multidimensional entangled states down conventional single-mode fiber (SMF). By entangling the spin-orbit degrees of freedom of a biphoton pair, passing the polarization (spin) photon down the SMF while accessing multiple orbital angular momentum (orbital) subspaces with the other, they realized multidimensional entanglement transport. They demonstrated transfer of multi-dimensional entanglement states over 250 m of single-mode fiber, showing that an infinite number of two-dimensional subspaces could be realized. […]

What a pair! Coupled quantum dots may offer a new way to store quantum information

Science Daily  January 29, 2020 An international team of researchers (USA – NIST, University of Maryland, Japan, Canada) created weakly coupled quantum dots by using the ultrasharp tip of a scanning tunneling microscope as a stylus hovering the tip above an ultracold sheet of graphene briefly increasing the voltage of the tip penetrating through the graphene into an underlying layer of boron nitride. It stripped electrons from atomic impurities in the layer and created electric charge which corralled freely floating electrons in the graphene, confining them to a tiny energy well. When a magnetic field of 4 to 8 tesla […]

In surprise breakthrough, scientists create quantum states in everyday electronics

Phys.org  December 9, 2019 An international team of researchers (USA – University of Chicago, Argonne National Laboratory, Chicago, Japan, Sweden, Hungary) has demonstrated they could electrically control quantum states embedded in silicon carbide. The quantum states in silicon carbide have the added benefit of emitting single particles of light with a wavelength near the telecommunications band which makes them well suited to long-distance transmission through the same fiber-optic network. They found that by using the diode, a one-way switch for electrons the quantum signal suddenly became free of noise and was almost perfectly stable mitigating the impurity issue. The work […]

A new alphabet to write and read quantum messages with very fast particles

Phys.org  September 2, 2019 If the quantum particle is relativistic it is impossible for standard techniques to decode the message unambiguously, and the communication therefore fails. Researchers in Austria deliver a new definition of the spin of quantum particles that move very quickly. It modifies both the way Anna writes the message and the way Bill reads it. Key to this technique is a “translation” of the way the message would be written and read between the standard alphabet used when the electron is at rest, and the new alphabet used when the electron travels very fast. These results indicate […]

Practical anonymous communication protocol developed for quantum networks

Phys.org  August 21, 2019 In the protocol developed by an international team of researchers (UK, USA – MIT, France) the player who wants to send a message anonymously notifies the receiver. Then, in each round of the protocol, an untrusted source creates an entangled quantum state called the Greenberger-Horne-Zeilinger (GHZ) state and distributes it between the players. Each player can either check if the state is actually the GHZ state by running a verification test or use the state for anonymous quantum communication. If test fails, there is possible breach, the misbehaving source is caught. If they use the state […]

Travelling towards a quantum internet at light speed

Science Daily  July 29, 2019 An international team of researchers (Japan, Germany) used laser light to send quantum information to a quantum dot by altering the spin state of a single electron trapped there. While electrons don’t spin in the usual sense, they do have angular momentum, which can be flipped when absorbing circularly polarized laser light. They were able to monitor the inter-dot charge tunneling which only occur when the photo-electron spin in one QD is anti-parallel to the electron spin in the other. The transfer of superposition states or entangled states allows for completely secure quantum key distribution […]

Secure quantum communications in the microwave range for the first time

Phys.org   June 19, 2019 An international team of researchers (Germany, Spain, Japan) conducted an experiment to develop a protocol for preparing a remote quantum state over a distance of 35 centimetres while conducting communication in the microwave regime. By employing propagating two-mode squeezed microwave states and feedforward, they achieved the remote preparation of squeezed states with up to 1.6 dB of squeezing below the vacuum level. They found nearly identical values for the entropy of the remotely prepared state and the respective conditional entropy given the classically communicated information and, thus, demonstrated close-to-perfect security…read more. Open Access TECHNICAL ARTICLE