Phys.org November 26, 2024 A fundamental requirement for quantum technologies is the ability to coherently control the interaction between electrons and photons. However, in many scenarios involving the interaction between light and matter, the exchange of linear or angular momentum between electrons and photons is not feasible, due to the dipole approximation limit. An international team of researchers (USA – University of Maryland, Italy, Spain, Germany, Japan, Australia) conceived a mechanism for such an orbital angular momentum transfer from optical vortex beams to electronic quantum Hall states. They identified a robust contribution to the radial photocurrent, in an annular graphene […]
Tag Archives: Quantum coherence
New method achieves tenfold increase in quantum coherence time via destructive interference of correlated noise
Phys.org July 10, 2024 Decoherence and imperfect control are crucial challenges for quantum technologies. Common protection strategies rely on noise temporal autocorrelation, which is not optimal if other correlations are present. An international team of researchers (Israel, Germany, USA – Caltech, industry) developed and experimentally demonstrated a strategy that used the cross-correlation of two noise sources. Utilizing destructive interference of cross-correlated noise extended the coherence time tenfold, improved control fidelity, and surpassed the state-of-the-art sensitivity for high frequency quantum sensing, significantly expanding the applicability of noise protection strategies… read more. Open Access TECHNICAL ARTICLE
Scientists demonstrate the survival of quantum coherence in a chemical reaction involving ultracold molecules
Phys.org May 16, 2024 Chemical reactions, where bonds break and form, are highly dynamic quantum processes. A fundamental question is whether coherence can be preserved in chemical reactions and then harnessed to generate entangled products. Researchers at Harvard University investigated this by studying the 2KRb → K2 + Rb2 reaction at 500 nK, focusing on the nuclear spin degrees of freedom. They prepared the initial nuclear spins in KRb in an entangled state by lowering the magnetic field to where the spin-spin interaction dominated and characterized the preserved coherence in nuclear spin wavefunction after the reaction. They observed an interference […]
Trillionths of a second: Photon pairs compress an electron beam into short pulses
Phys.org June 19, 2023 Researchers in Germany used nonlinear-optical two-photon transitions for the quantum-coherent control of a free-electron matter wave in free space. They superimposed an electron beam with two crossed laser beams of different photon energies for non-linear Compton scattering. At suitable angle combinations, the electron energy spectrum became modulated into discrete energy sidebands with thousands of interference maxima. They explained their observations by the cascaded addition and subtraction of two-photon pairs under three-body conservation of energy and momentum. Calculations revealed that the electron matter wave converted into pulses of few-attosecond duration. According to the researchers their work provides […]
Environmental noise paradoxically preserves the coherence of a quantum system
Phys.org May 30, 2018 Normally dephasing causes decoherence in quantum systems. An international team of researchers (Japan, Germany, USA – University of Buffalo, University of Michigan) shows a scheme of entanglement engineering where pure dephasing assists the generation of quantum entanglement at distant sites in a chain of electron spins confined in semiconductor quantum dots. One party of an entangled spin pair, prepared at a single site, is transferred to the next site and then adiabatically swapped with a third spin using a transition across a multi-level avoided crossing. This process is accelerated by the noise-induced dephasing… read more. Open […]