Phys.org January 28, 2022 Trapped ions excited with a laser beam can be used to create entangled qubits in quantum information systems but addressing several stationary pairs of ions in a trap requires multiple optical switches and complex controls. Researchers at Georgia Tech Research Institute moved calcium ions held in a surface electrode trap through a stationary bichromatic optical beam potentially integrating the existing transport control into quantum logic operations. Measurements showed that the entangled quantum state of the two qubits transported through the optical beam had a fidelity comparable to entangled states produced by stationary gates performed in the […]
Tag Archives: Quantum computing
A new method for quantum computing
Phys.org January 31, 2022 Using trapped-ion platform and optical tweezers researchers in the Netherlands have constructed new building blocks for quantum computing that pose fewer technical difficulties than current state-of-the art methods. Since the electric field allows for long-range qubit-qubit interactions mediated by the center-of-mass motion of the ion crystal alone, it is inherently scalable to large ion crystals. The proposed scheme does not rely on ground-state cooling. They studied the effects of imperfect cooling of the ion crystal, as well as the role of unwanted qubit-motion entanglement, and discuss the prospects of implementing the state-dependent tweezers in the laboratory… […]
Experimental quantum teleportation of propagating microwaves
Phys.org January 4, 2022 Recent breakthroughs in quantum computation with superconducting circuits trigger a demand for quantum communication channels between spatially separated superconducting processors operating at microwave frequencies. An international team of researchers (Germany, Austria) demonstrated the unconditional quantum teleportation of propagating coherent microwave states by exploiting two-mode squeezing and analog feedforward over a macroscopic distance of d = 0.42 m. They achieved a teleportation fidelity of F = 0.689 ± 0.004, exceeding the asymptotic no-cloning threshold. Thus, the quantum nature of the teleported states is preserved, opening the avenue toward unconditional security in microwave quantum communication. As their principal teleportation […]
Shrinking qubits for quantum computing with 2D materials
Nanowerk December 1, 2021 The capacitor electrodes that comprise the qubits in quantum computers must be large to avoid lossy dielectrics. This hinders scaling degrading individual qubit addressability and limiting the spatial density of qubits. An international team of researchers (USA – Columbia University, Raytheon BBN Technologies, Japan) took advantage of the unique properties of van der Waals (vdW) materials to reduce the qubit area by >1000 times while preserving the capacitance while maintaining quantum coherence. The qubits combine conventional aluminum-based Josephson junctions with parallel-plate capacitors composed of crystalline layers of superconducting niobium diselenide and insulating hexagonal boron nitride. The […]
Cooling radio waves to their quantum ground state
Phys.org October 15, 2021 In standard cryogenic systems thermal decoherence prevents access to the quantum regime for photon frequencies below the gigahertz domain. An international team of researchers (the Netherlands, Germany) engineered two superconducting LC circuits coupled by a photon-pressure interaction and demonstrated sideband cooling of a hot radio frequency (RF) circuit using a microwave cavity. Because of a substantially increased coupling strength, they obtained a large single-photon quantum cooperativity and reduced the thermal RF occupancy by 75% with less than one pump photon. For larger pump powers, the coupling rate exceeds the RF thermal decoherence rate by a factor […]
Achilles heel of graphene exposed
Nanowerk July 19, 2021 The quantum Hall effect is the seminal example of topological protection as charge carriers are transmitted through one-dimensional edge channels where backscattering is prohibited. In conventional Hall bar geometries, topological protection of graphene edge channels is found less robust than in high mobility semi-conductors. An international team of researchers (Belgium, Germany, Japan) exploring graphene quantum Hall regime at the local scale revealed that the detrimental influence of antidots along the graphene edges, mediating backscattering towards upstream edge channels triggering topological breakdown. The finding is a major step forward in the understanding of the quantum Hall effect […]
Researchers uncover unique properties of a promising new superconductor
Science Daily June 16, 2021 An international team of researchers (USA – University of Minnesota, Pennsylvania State University, Cornell University, National High Magnetic Field Laboratory, China, Switzerland) found that Niobium diselenide (NbSe2) in 2D form is a more resilient superconductor because it has a two-fold symmetry, which is very different from thicker samples of the same material. Despite the six-fold structure, it only showed two-fold behavior in the experiment. They attributed the newly discovered two-fold rotational symmetry of the superconducting state in NbSe2 to the mixing between two closely competing types of superconductivity, namely the conventional s-wave type — typical of […]
Light meets superconducting circuits
EurekAlert May 10, 2021 Realizing the full potential of quantum computers requires a significant increase in the number of qubits to store and manipulate quantum information. To prevent contaminating quantum signals by thermal noise, the superconducting quantum systems must operate at ultra-low temperatures. An international team of researchers (Switzerland, India) has developed a novel approach that uses light to read out superconducting circuits. They replaced low-noise high-electron mobility transistors and coaxial cables with a lithium niobate electro-optical phase modulator and optical fibers. Microwave signals from superconducting circuits modulate a laser carrier and encode information on the output light at cryogenic […]
Twistoptics: A new way to control optical nonlinearity
Science Daily March 4, 2021 A hot topic in the field of 2D materials has been exploring how twisting can change the electronic properties of the layered system. van der Waals (vdW) heterostructures feature layers that can be stacked at arbitrary angles, giving complete control over the presence or lack of inversion symmetry at a crystal interface. An international team of researchers (USA – Columbia University, industry, Germany, Japan) demonstrated highly tunable second harmonic generation (SHG) using bulk hexagonal boron nitride crystals and introduced the term twistoptics to describe studies of optical properties in twistable vdW systems. By suppressing residual […]
A speed limit also applies in the quantum world
Science Daily February 19, 2021 In two-level systems, the quantum brachistochrone solutions are long known but they are not applicable to larger systems, especially when the target state cannot be reached through a local transformation. An international team of researchers (Germany, USA – MIT, Italy) has demonstrated fast coherent transport of an atomic wave packet over 15 times its size, a case of quantum processes going beyond the two-level system. The measurements of the transport fidelity revealed the existence of a minimum duration—a quantum speed limit—for the coherent splitting and recombination of matter waves. They obtained physical insight into this […]