Phys.org October 10, 2023 An international team of researchers (Germany, Austria) developed a deployable free-space QKD system and demonstrated its use in realistic scenarios. They developed and launched a low-Earth-orbit satellite for implementing decoy-state QKD—a form of QKD that uses weak coherent pulses at high channel loss and was secure because photon-number-splitting eavesdropping could be detected. They achieved a kilohertz key rate from the satellite to the ground over up to 1,200 kilometres. The key rate was around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. According to the researchers their work […]
Tag Archives: Quantum networks
A simpler way to connect quantum computers
Science Daily August 30, 2023 Recently, there has been significant interest in rare earth ions, in particular Er3+ for its telecom band optical transition that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Researchers at Princeton University implanted Er3+ into CaWO4 to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, they observed single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth […]
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 […]
Cooling matter from a distance
Science Daily February 2, 2022 Researchers in Switzerland succeeded in forming a control loop consisting of two quantum systems separated by one meter. Within this loop a vibrating membrane was cooled by a cloud of atoms, and the two systems were coupled to one another by laser light. As one of the systems acts as a control unit for the other, no measurement is needed. Instead, the control system is configured to bring the target system into a desired state by means of coherent quantum mechanical interaction. They successfully used this coherent feedback mechanism to reduce the temperature of the […]
The era of single-spin color centers in silicon carbide is approaching
Phys.org July 19, 2021 The spin color centers in silicon carbide, including silicon vacancies and divacancies have excellent optical and spin properties. Researchers in China have presented the coherent manipulation of single divacancy spins in 4H-SiC with a high readout contrast (−30%) and a high photon count rate under ambient conditions, which are competitive with the nitrogen-vacancy centres in diamond. Coupling between a single defect spin and a nearby nuclear spin is also observed. They provided a theoretical explanation for the high readout contrast by analysing the defect levels and decay paths. Since the high readout contrast is important in […]
When memory qubits and photons get entangled
Phys.org March 15, 2021 The implementation of efficient interfaces between photons and stationary qubits is crucial for the rate of information transfer and the scalability of a quantum network. With their experimental setup researchers in Germany demonstrated quantum entanglement between a stationary qubit and a photon out of an optical fiber resonator. They showed the generation of deterministic entanglement at a high fidelity of 90.1(17)% between a trapped Yb ion and a photon emitted into the resonator mode. And achieved a success probability for generation and detection of entanglement for a single shot of 2.5 × 10−3 resulting in 62 Hz entanglement rate. […]
Quantum entanglement realized between distant large objects
Phys.org September 28, 2020 The disparity of hybrid systems and the vulnerability of quantum correlations have thus far hampered the generation of macroscopic hybrid entanglement. An international team of researchers (Spain, USA – University of Chicago, Denmark) generated an entangled state between the motion of a macroscopic mechanical oscillator and a collective atomic spin oscillator, as witnessed by an Einstein–Podolsky–Rosen variance below the separability limit, 0.83 ± 0.02 < 1. The mechanical oscillator is a millimetre-size dielectric membrane, and the spin oscillator is an ensemble of 109 atoms in a magnetic field. Light propagating through the two spatially separated systems […]
A quantum memory that operates at telecom wavelengths
Phys.org June 15, 2020 Researchers in the Netherlands designed and fabricated the fully engineerable, device with operational wavelength of 1550 nanometers to enable the system to work in the low-loss telecommunication band wavelength. The system’s optical and mechanical resonances are fully artificial. They were able to show that the memory has a satisfactory lifetime and coherence while successfully creating the superposition state. In future studies, they plan to gain a better understanding of why the de-phasing of a quantum state, to avoid having such a short coherence, understand the underlying microscopic mechanisms, and increase the overall efficiency of the memory. […]
Light from stretchable sheets of atoms for quantum technologies
EurekAlert April 16, 2020 Unlike other nanomaterials used as quantum light sources, such as diamond, silicon carbide or gallium nitride hexagonal boron nitride is not brittle and comes with the unique stretchable mechanical properties of a van der Waals crystal. However, their spectral inhomogeneity currently limits their potential applications. Researchers in Australia applied tensile strain to quantum emitters embedded in few‐layer hBN films. They observed both red and blue spectral shifts with tuning magnitudes up to 65 meV. Rotation of the optical dipole in response to strain suggested the presence of a second excited state. They developed a theoretical model […]