Physicists discover a unique quantum behavior that offers a new way to manipulate electron-spin and magnetization to push forward cutting-edge spintronic technologies, like neuromorphic computing.
Category: quantum physics – Page 10
Symmetry plays a crucial role in understanding fundamental phenomena such as conservation laws, the classification of phases of matter, and their transitions. Recently, researchers have been exploring ways to manipulate symmetries in quantum many-body systems with time-dependent driving protocols and, in particular, engineering new symmetries that do not naturally occur. This significantly enriches the toolbox for quantum simulation and computation, and has led to many exciting discoveries of nonequilibrium phases such as discrete time crystals. However, controlling multiple symmetries—especially in a simple and experimentally friendly way—has remained a challenge. In this work, we propose a novel method to engineer hierarchical symmetries by time-dependent protocols.
By carefully controlling how symmetry-indicating observables evolve over time, we show how to create a sequence of symmetries that emerge one after another, each with distinct properties. Our method relies on a recursive construction that hierarchically minimizes the effects of symmetry-breaking processes. This leads to a corresponding sequence of prethermal steady states with controllable lifetimes, each exhibiting a lower symmetry than the preceding one. We illustrate this protocol with several examples, demonstrating how different types of order can emerge through hierarchical symmetry breaking.
This toolbox of hierarchical symmetries opens a new path to stabilizing quantum states and controlling unwanted symmetry-breaking effects, which can be particularly useful in quantum computing and quantum simulation. The construction applies to classical and quantum, fermionic and bosonic, interacting and noninteracting systems. The underlying mechanism generalizes state-of-the-art dynamical decoupling techniques and is implementable on present-day quantum simulation platforms.
US researchers send quantum entangled signal over commercial fiber optic network without requiring any downtime, a major achievement.
A huge number of ultracold atoms have been corralled into a grid that could form the basis of the next largest quantum computer.
The operation and performance of quantum computers relies on the ability to realize and control entanglement between multiple qubits. Yet entanglement between many qubits is inherently susceptible to noise and imperfections in quantum gates.
In recent years, quantum physicists and engineers worldwide have thus been trying to develop more robust protocols to realize and control entanglement. To be most effective for real-world applications, these approaches should reliably support long-range entanglement, or in other words ensure that qubits remain entangled even when they are separated by large distances.
Researchers at IBM Quantum, University of Cologne and Harvard University set out to demonstrate one of these protocols in an experimental setting.
Physicists have spent more than a century measuring and making sense of the strange ways that photons, electrons, and other subatomic particles interact at extremely small scales. Engineers have spent decades figuring out how to take advantage of these phenomena to create new technologies.
In one such phenomenon, called quantum entanglement, pairs of photons become interconnected in such a way that the state of one photon instantly changes to match the state of its paired photon, no matter how far apart they are.
Nearly 80 years ago, Albert Einstein referred to this phenomenon as “spooky action at a distance.” Today, entanglement is the subject of research programs across the world—and it’s becoming a favored way to implement the most fundamental form of quantum information, the qubit.
Quantum computing promises to solve complex problems exponentially faster than a classical computer, by using the principles of quantum mechanics to encode and manipulate information in quantum bits (qubits).
Qubits are the building blocks of a quantum computer. One challenge to scaling, however, is that qubits are highly sensitive to background noise and control imperfections, which introduce errors into the quantum operations and ultimately limit the complexity and duration of a quantum algorithm. To improve the situation, MIT researchers and researchers worldwide have continually focused on improving qubit performance.
In new work, using a superconducting qubit called fluxonium, MIT researchers in the Department of Physics, the Research Laboratory of Electronics (RLE), and the Department of Electrical Engineering and Computer Science (EECS) developed two new control techniques to achieve a world-record single-qubit fidelity of 99.998%. This result complements then-MIT researcher Leon Ding’s demonstration last year of a 99.92% two-qubit gate fidelity.
Science is always looking for more computing power and more efficient tools capable of answering its questions. Quantum computers are the new frontier in data processing, as they use the quantum properties of matter, such as the superposition of states and entanglement, to perform very complex operations.
A research team coordinated by the Department of Physics of the University of Trento had the opportunity to test some hypotheses on confinement in Z2 lattice gauge theory on the quantum computers of Google’s Quantum Artificial Intelligence Lab, in California. Their work was published in Nature Physics.
Gauge theories describe the fundamental forces in the standard model of particle physics and play an important role in condensed matter physics. The constituents of gauge theories, such as charged matter and electric gauge field, are governed by local gauge constraints, which lead to key phenomena that are not yet fully understood. In this context, quantum simulators may offer solutions that cannot be reached using conventional computers.
Continuous automatic polarization channel stabilization from heterodyne detection of coexisting dim reference signals
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Quantum networking continues to encode information in polarization states due to ease and precision. The variable environmental polarization transformations induced by deployed fiber need correction for deployed quantum networking. Here, we present a method for automatic polarization compensation (APC) and demonstrate its performance on a metropolitan quantum network. Designing an APC involves many design decisions as indicated by the diversity of previous solutions in the literature. Our design leverages heterodyne detection of wavelength-multiplexed dim classical references for continuous high-bandwidth polarization measurements used by newly developed multi-axis (non-)linear control algorithm(s) for complete polarization channel stabilization with no downtime. This enables continuous relatively high-bandwidth correction without significant added noise from classical reference signals. We demonstrate the performance of our APC using a variety of classical and quantum characterizations. Finally, we use C-band and L-band APC versions to demonstrate continuous high-fidelity entanglement distribution on a metropolitan quantum network with an average relative fidelity of 0.94 ± 0.03 for over 30 hrs.
A team of physicists led by The City College of New York’s Lia Krusin-Elbaum has developed a novel technique that uses hydrogen cations (H+) to manipulate relativistic electronic bandstructures in a magnetic Weyl semimetal—a topological material where electrons mimic massless particles called Weyl fermions. These particles are distinguished by their chirality or “handedness” linked to their spin and momentum.
In the magnetic material MnSb₂Te₄, researchers unveiled a fascinating ability to “tune” and enhance the chirality of electronic transport by introducing hydrogen ions, reshaping on-demand the energy landscapes—called Weyl nodes—within the material. This finding could open a breadth of new quantum device platforms for harnessing emergent topological states for novel chiral nano-spintronics and fault-tolerant quantum computing. Entitled “Transport chirality generated by a tunable tilt of Weyl nodes in a van der Waals topological magnet,” the study appears in the journal Nature Communications.
The tuning of Weyl nodes with H+ heals the system’s (Mn-Te) bond disorder and lowers the internode scattering. In this process—which The City College team tests in the Krusin Lab using angularly-resolved electrical transport—electrical charges move differently when the in-plane magnetic field is rotated clockwise or counterclockwise, generating desirable low-dissipation currents. The reshaped Weyl states feature a doubled Curie temperature and a strong angular transport chirality synchronous with a rare field-antisymmetric longitudinal resistance—a low-field tunable ‘chiral switch’ that is rooted in the interplay of topological Berry curvature, chiral anomaly and a hydrogen-mediated form of Weyl nodes.