Phys.org August 26, 2022 Measurement and feedback control are essential features of quantum science, with applications ranging from quantum technology protocols to information-to-work conversion in quantum thermodynamics. Theoretical descriptions of feedback control are typically given in terms of stochastic equations requiring numerical solutions or are limited to linear feedback protocols. An international team of researchers (Sweden, USA – University of Maryland, Switzerland) presented a formalism for continuous quantum measurement and feedback, both linear and nonlinear. The main result is a quantum Fokker-Planck master equation describing the joint dynamics of a quantum system and a detector with finite bandwidth. For fast […]
Category Archives: Quantum technology
Exploring quantum electron highways with laser light
Nanowerk August 18, 2022 The phase transition between non-trivial and trivial topological states is important for next-generation technology, such as dissipation-free electronics. A team of researchers in the US (SLAC National Accelerator Laboratory, Stanford University, Harvard University, the State University of New Jersey) has demonstrated that circularly polarized laser-field-driven high-harmonic generation is distinctly sensitive to the non-trivial and trivial topological phases in the prototypical three-dimensional topological insulator bismuth selenide. The phase transition is chemically initiated by reducing the spin–orbit interaction strength through the substitution of bismuth with indium atoms. The phase transition is chemically initiated by reducing the spin–orbit interaction […]
Physicists harness quantum ‘time reversal’ to measure vibrating atoms
Phys.org July 14, 2022 Linear quantum measurements with independent particles are bounded by the standard quantum limit, which limits the precision achievable in estimating unknown phase parameters. The standard quantum limit can be overcome by entangling the particles, but the sensitivity is often limited by the final state readout, especially for complex entangled many-body states with non-Gaussian probability distributions. By implementing an effective time-reversal protocol in an optically engineered many-body spin Hamiltonian a team of researchers in the US (MIT, Harvard University) has demonstrated a quantum measurement with non-Gaussian states with performance beyond the limit of the readout scheme. This […]
Researchers create order from quantum chaos
Phys.org July 19, 2022 A team of researchers in the US (National Energy Research Laboratory, University of Colorado, University of Kentucky) selected a tetracenethiophene compound called TES TIPS-TT, which has a crystal structure in which all molecules share a common axis. Using time-resolved paramagnetic resonance spectroscopy they characterized the spin state of the electrons in the material. The observed spin sublevel populations are consistent with predictions from the JDE model, including preferential 5TT0 formation at z ‖ B0, with one caveat—two 5TT spin sublevels have little to no population. This may be due to crossings between the 5TT and 3TT […]
New hardware integrates mechanical devices into quantum tech
Phys.org April 22, 2022 Proposals to combine microwave-frequency mechanical resonators with superconducting devices suggest the possibility of powerful quantum acoustic processors. At present the acoustic platforms lack processors capable of controlling the quantum states of several mechanical oscillators with a single qubit and the rapid quantum non-demolition measurements of mechanical states needed for error correction. Researchers at Stanford University used a superconducting qubit to control and read out the quantum state of a pair of nanomechanical resonators. Their device is capable of fast qubit–mechanics swap operations, which they used to deterministically manipulate the mechanical states. By placing the qubit into […]
Squeezing the noise out of microscopes with quantum light
Nanowerk February 14, 2022 Quantum microscopy relies on extremely delicate control of light waves. However, its sensitivity is typically limited by optical losses. A team of researchers in the US (Oak Ridge National Laboratory, Tulane University, MIT, University of Colorado) circumvented the problem with an entangled light called squeezed light, that is, the intensities of the light beams are correlated with each other at the quantum level resulting in noise reduction of up to 3 dB below the standard quantum limit. They minimized the photon backaction noise while taking advantage of quantum noise reduction by transducing the cantilever displacement signal […]
Researchers find new way of gaining quantum control from loss
Phys.org January 24, 2022 Researchers in China implemented dissipative spin–orbit-coupled bands filled with ultracold fermions and observed parity-time symmetry breaking as a result of the competition between the spin–orbit coupling and dissipation. Tunable dissipation, introduced by state-selective atom loss, enabled them to tune the energy gap and close it at the critical dissipation value, the so-called exceptional point. Near the critical point, the state evolution exhibited a chiral response, which enabled them to tune the spin–orbit coupling and dissipation dynamically, revealing topologically robust chiral spin transfer when the quantum state encircled the exceptional point. According to the researchers this demonstrates […]
New materials for quantum technologies
Phys.org December 22, 2021 To advance spintronics devices and quantum information technology using materials with non-trivial topological properties, three key challenges are still unresolved – the identification of topological band degeneracies located at the Fermi level, the ability to easily control such topological degeneracies., and the identification of generic topological degeneracies in large, multisheeted Fermi surfaces. Researchers in Germany have shown that the non-symmorphic symmetries in chiral, ferromagnetic manganese silicide (MnSi) generate nodal planes (NPs) which enforce topological protectorates (TPs) with substantial Berry curvatures at the intersection of the NPs with the Fermi surface (FS) regardless of the complexity of […]
To capture single photons, researchers create an interference ‘wall’
Phys.org December 3, 2021 Creating entangled photons can be a difficult task requiring a complicated setup as non-classical kinds of light have a small number of photons. In a new scheme researchers at the University of Chicago used two different sources to simultaneously emit photons into a cavity that has an extremely weak nonlinearity. With careful tuning, these sources then cancel each other out with destructive interference—creating a “wall” that blocks photons—once the selected number of photons are captured in the cavity. The basic mechanism can also be applied to all electromagnetic radiation. It can be used to generate and […]
All-nitride superconducting qubit made on a silicon substrate
Science Daily September 20, 2021 Researchers in Japan have developed superconducting qubits based on NbN/AlN/NbN epitaxial Josephson junctions on silicon substrates which promise to overcome the drawbacks of qubits based on Al/AlOx/Al junctions. The all-nitride qubits have great advantages such as chemical stability against oxidation, resulting in fewer two-level fluctuators, feasibility for epitaxial tunnel barriers that reduce energy relaxation and dephasing, and a larger superconducting gap of ~5.2 meV for NbN, compared to ~0.3 meV for aluminum, which suppresses the excitation of quasiparticles. By replacing conventional MgO by a silicon substrate with a TiN buffer layer for epitaxial growth of […]