Phys.org April 15, 2024 Nonlocality is crucial for device-independent technologies like quantum key distribution and randomness generation. It quickly deteriorates in the presence of noise, and restoring nonlocal correlations requires additional resources incurring a significant resource overhead. An international team of researchers (Australia, France, USA – NIST, Boulder, CO) experimentally demonstrated that single copies of Bell-local states, incapable of violating any standard Bell inequality, could give rise to nonlocality after being embedded into a quantum network of multiple parties. They subjected the initial entangled state to a quantum channel that broadcast part of the state to two independent receivers and […]
Tag Archives: Quantum communication
The world is one step closer to secure quantum communication on a global scale
Phys.org March 25, 2024 An on-demand source of bright entangled photon pairs is needed for quantum key distribution (QKD) and quantum repeaters. The generation of such pairs is based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, SPDC pair extraction efficiency is very limited when operating at near-unity fidelity. In principle quantum dots in photonic nanostructures can overcome this limit, but the devices with high entanglement fidelity have low pair extraction efficiency. An international team of researchers (Canada, the Netherlands, Sweden) has demonstrated a measured peak entanglement fidelity of 97.5% ± 0.8% and pair extraction efficiency of 0.65% from an InAsP […]
Research team takes a fundamental step toward a functioning quantum internet
Phys.org February 7, 2024 Quantum repeater networks require independent absorptive quantum memories capable of storing and retrieving indistinguishable photons to perform high-repetition entanglement swapping operations. An international team of researchers (USA – Stony Brook University, industry, Brookhaven National Laboratory, Italy) performed Hong-Ou-Mandel (HOM) interference between photonic polarization states and single-photon-level pulses stored and retrieved from two sets of independent room-temperature quantum memories. They showed that the storage and retrieval of polarization states from quantum memories did not degrade the HOM visibility for few-photon-level polarization states in a dual-rail configuration. For single-photon-level pulses, they measured the HOM visibility with various levels […]
A linear path to efficient quantum technologies
Nanowerk September 12, 2023 Bell-state projections serve as a fundamental basis for most quantum communication and computing protocols today. However, with current Bell-state measurement schemes based on linear optics, only two of four Bell states can be identified, which means that the maximum success probability of this vital step cannot exceed 50%. Researchers in Germany experimentally demonstrated a scheme that amended the original measurement with additional modes in the form of ancillary photons, which led to a more complex measurement pattern, and ultimately a higher success probability of 62.5%. Experimentally, they achieved a success probability of (57.9 ± 1.4)%, a […]
New quantum device generates single photons and encodes information
Science Daily August 24, 2023 Quantum light emitters capable of generating single photons with circular polarization and non-classical statistics could enable non-reciprocal single-photon devices and deterministic spin–photon interfaces for quantum networks. The emission of chiral quantum light relies on the application of intense external magnetic fields, electrical/optical injection of spin-polarized carriers/excitons or coupling with complex photonic metastructures. An international team of researchers (USA – Los Alamos National Laboratory, Switzerland) stacked a single-molecule-thick layer of tungsten diselenide semiconductor onto a thicker layer of nickel phosphorus trisulfide magnetic semiconductor and created a series of nanometer-scale indentations on the thin stack of materials. […]
New technology developed for quantum cryptography applications
Phys.org May 10, 2023 Temporal modes (TMs), an encoding basis based on the time-frequency degree of freedom of photons, represent one of the most promising high-dimensional alphabets. TM-based quantum communication has until now been limited to a two-dimensional space due to the lack of a suitable decoder. However, quantum communication protocols based on single-photon TMs require suitable multichannel decoders. Researchers in Germany have demonstrated a new device that facilitates demultiplexing of high-dimensional TMs of single photons, and implemented a complete five-dimensional decoder that enables TM-based high-dimensional quantum key distribution. They showed that it is possible to scale the presented decoder […]
Using the power of symmetry for new quantum technologies
Phys.org December 15, 2022 In previous research, only one waveguide has been coupled to the qubit with limited access to its symmetries. Researchers in Sweden used two waveguides. They demonstrated a novel coupling scheme between an artificial molecule comprising two identical, strongly coupled transmon qubits and two microwave waveguides. The coupling was engineered so that transitions between states of the same symmetry, with respect to the permutation operator, are predominantly coupled to one waveguide. The coupling selectivity exceeded by a factor of 30 for both waveguides in their device. They showed that it can be used to coherently couple states […]
On-demand storage of photonic qubits at telecom wavelengths
Phys.org December 6, 2022 Researchers in China processed a fiber-integrated quantum memory at telecom wavelengths based on a laser-written waveguide fabricated in an erbium-doped yttrium silicate. Both ends of the waveguide memory were directly connected with fiber arrays with a fiber-to-fiber efficiency of 51%. Storage fidelity of 98.3(1)% was obtained for time-bin qubits encoded with single-photon-level coherent pulses, which is far beyond the maximal fidelity that can be achieved with a classical measure and prepared strategy. This device featured high reliability and easy scalability, and it can be directly integrated into fiber networks, which could play an essential role in […]
New measurements quantifying qudits provide glimpse of quantum future
Science Daily October 13, 2022 An international team of researchers (USA – Oak Ridge National Laboratory, Purdue University, industry, Switzerland) combined state-of-the-art frequency-bin production with state-of-the-art light sources to develop an effective technique to characterize high-dimensional qudit entanglement. They fully characterized an entangled pair of eight-level qudits, which formed a 64-dimensional quantum space — quadrupling the previous record for discrete frequency modes. The researchers began their experiments by shining a laser into a micro-ring resonator — a circular, on-chip device fabricated and designed to generate nonclassical light. This powerful photon source which took 1 square millimeter of space and allowed […]
Quantum Entanglement Has Now Been Directly Observed at The Macroscopic Scale
Science Alert October 16, 2022 To date, entanglement has generally been limited to microscopic quantum units such as pairs or multiples of single ions, atoms, photons, and so on. Previous studies had also reported on macroscopic quantum entanglement, all the necessary measurements were recorded rather than inferred, and the entanglement was generated in a deterministic, non-random way. An international team of researchers (Finland, Australia) have shown how it’s possible to measure the position and momentum of the two drumheads at the same time, getting around Heisenberg’s Uncertainty Principle working with macroscopic drums (oscillators) in a state of quantum entanglement. In […]