MIT News April 29, 2020 In a new book, “Quantum Legacies: Dispatches from an Uncertain World,” Professor David Kaiser of MIT describes dramatic shifts in the history of an evolving discipline. Moving between vignettes of key physicists, original research about the growth of the field, and accounts of his own work in cosmology, the author emphasizes the vast changes in the field over time…read more. Book: “Quantum Legacies: Dispatches from an Uncertain World”

# Category Archives: Quantum science

# New protocol identifies fascinating quantum states

Phys.org April 10, 2020 An international team of researchers (Austria, USA – NIST, University of Maryland, Germany, France) proposed and analyzed a universal toolbox of measurement protocols to reveal many-body topological invariants of phases with global symmetries, which can be implemented in state-of-the-art experiments with synthetic quantum systems, such as Rydberg atoms, trapped ions, and superconducting circuits. The protocol is based on extracting the many-body topological invariants from statistical correlations of randomized measurements, implemented with local random unitary operations followed by site-resolved projective measurements. They illustrated the technique and its application in the context of the complete classification of bosonic […]

# Does relativity lie at the source of quantum exoticism?

Phys.org April 2, 2020 In quantum mechanics inherent randomness happens without any cause. Randomness that appears in non-relativistic quantum theory tacitly respects relativity, for example, it makes instantaneous signaling impossible. An international team of researchers (Poland, Singapore, UK) argues that this is because the special theory of relativity can itself account for such a random behavior. They show that the full mathematical structure of the Lorentz transformation, the one which includes the superluminal part, implies the emergence of non-deterministic dynamics, together with complex probability amplitudes and multiple trajectories. This indicates that the connections between the two seemingly different theories are […]

# Quantum-entangled light from a vibrating membrane

Phys.org March 31, 2020 Optical quantum states propagate with ultralow attenuation and resilient to ubiquitous thermal noise. Mechanical systems are envisioned as versatile interfaces between photons and a variety of solid-state quantm information processing platforms. Researchers in Denmark generated entanglement between two propagating optical modes by coupling them to the same cryogenic mechanical system. The entanglement persisted at room temperature. They verified the inseparability of the bipartite state and fully characterized its logarithmic negativity by homodyne tomography. Combined with quantum interfaces between mechanical systems and solid-state qubit processors, this paves the way for mechanical systems enabling long-distance quantum information networking […]

# Scientists Find Yet Another Way to Get Qubits Working at Room Temperature

Science Alert March 22, 2020 Defect-based quantum systems are often complicated by charge-state instabilities and interference by phonons, which can diminish spin-initialization fidelities and limit room-temperature operation. An international team of researchers (Hungary, Sweden, USA – Argonne National Laboratory, University of Chicago, IBM, Russia) has identified a pathway around these drawbacks by showing that an engineered quantum well can stabilize the charge state of a qubit. Using density-functional theory and experimental synchrotron X-ray diffraction studies they constructed a model for previously unattributed point defect centers in silicon carbide as a near-stacking fault axial divacancy and showed how this model explains […]

# Influential electrons? Physicists uncover a quantum relationship

Science Daily January 13, 2020 Topological insulators’ surface states can be manipulated by the interface environment to display various emergent phenomena. An international team of researchers (New York University, Lawrence Berkeley National Laboratory, University of Pennsylvania, Rutgers University, MIT) used spectromicroscopy, which can track how the motion of surface electrons differs from region to region within a material, to study bismuth selenide collecting data from nearly 1,000 smaller regions. They observed signatures of quantum hybridization in the relationships between moving electrons, such as a repulsion between electronic states that come close to one another in energy. Measurements from this method […]

# Heat energy leaps through empty space, thanks to quantum weirdness

Phys.org December 11, 2019 Recent theory has predicted that quantum fluctuations of electromagnetic fields could induce phonon coupling across a vacuum and thereby facilitate heat transfer. Researchers at UC Berkeley experimentally demonstrated heat transfer induced by quantum fluctuations between two objects separated by a vacuum gap. They used nanomechanical systems to realize strong phonon coupling through vacuum fluctuations and observed the exchange of thermal energy between individual phonon modes. The experimental observation agrees well with their theoretical calculations and is unambiguously distinguished from other effects such as near-field radiation and electrostatic interaction…read more. TECHNICAL ARTICLE

# A technique to measure mechanical motion beyond the quantum limit

Phys.org November 20, 2019 Through the interaction of the mechanical oscillator with a microwave (or optical) cavity, back-action evading measurement in principle enables noiseless measurement of the position of the mechanical oscillator. However, additional interactions between the microwave (or optical) field and the mechanical oscillator lead to instabilities in mechanical motion, which prevents continuous measurement. Through simultaneous but unequal electromechanical amplification and cooling processes, a team of researchers in the US (industry, University of Colorado, NIST) created a method for a nearly noiseless pulsed measurement of mechanical motion. The conversion of signals between these two disparate frequency bands is important […]

# Achieving quantum supremacy

Science Daily October 23, 2019 Using 53 entangled qubits an international team of researchers (USA – Google, UMass Amherst, NASA, Caltech, UC Santa Barbara, Oak Ridge National Laboratory, UC Riverside, industry, Germany) has solved a problem that would take 10,000 years on a classical supercomputer in 200 seconds on their quantum computer. The algorithm was chosen to emphasize the strengths of the quantum computer by leveraging the natural dynamics of the device. They used a method called cross-entropy benchmarking to compare the quantum circuit’s output (a “bitstring”) to its corresponding ideal probability computed via simulation on a classical computer to […]

# In a Quantum First, Physicists Put 2,000 Atoms in Two Places at Once

Science Alert October 5, 2019 An international team of researchers (Austria, Switzerland, Germany) has demonstrated the interference of a molecular library of functionalized oligoporphyrins consisting of up to 2,000 atoms, by far the heaviest objects shown to exhibit matter-wave interference to date. They realized quantum superposition of these massive particles by measuring interference fringes in a new 2-m-long interferometer that permits access to a wide range of particle masses with a large variety of internal states. The results show excellent agreement with quantum theory and cannot be explained classically. The interference fringes reach more than 90% of the expected visibility […]