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Category: quantum physics – Page 4

A Map to a Long-Sought Quantum Simulator

The Sachdev-Ye-Kitaev (SYK) model describes information scrambling in black holes and an unusual metallic phase in high-temperature superconductors. Despite those and other far-reaching applications, realizing the model in the lab has been extremely challenging because the particle interactions required are intricate and long-ranged. Now Charles Creffield at the Complutense University of Madrid and his colleagues have detailed how this model could be simulated in existing cold-atom setups [1]. Their strategy provides a practical path to exploring quantum phenomena that are currently confined to theory.

Rather than engineer the requisite particle interactions from the outset, the team started with a much simpler setup emulating the Hubbard model, which is used to understand how electrons moving in a lattice give rise to superconductivity and other phenomena. Ultracold atoms are placed in a one-dimensional optical lattice, where they hop between lattice sites and mutually repel each other when occupying the same site. The lattice is then periodically shaken to make the rate of hopping oscillate in time. This modulation suppresses the atoms’ ordinary motion and generates effective interactions between all the atoms at once, closely resembling the particle behavior of the SYK model.

Using detailed numerical simulations, the researchers went on to show that their Hubbard-based system reproduces several key features of the SYK model, including its characteristic chaotic dynamics and fast spreading of quantum information. The team emphasizes that its approach could be enacted straightforwardly using currently available cold-atom technologies. Such an implementation would offer a controlled, versatile platform for simulating the SYK model and possibly for probing the uncertain physics of quantum chaos and quantum gravity.

New technique enables LIGO to peer farther into the distant universe

Scientists at the University of California, Riverside, have developed a new way to help gravitational-wave observatories see farther into the universe by solving one of their biggest challenges: tiny heat-induced distortions in the massive mirrors at the heart of the detectors.

The technique, described in a paper published in Classical and Quantum Gravity, uses thermal imaging to reveal microscopic distortions caused by powerful lasers. By measuring those distortions more precisely, observatories such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) could improve their sensitivity and detect weaker, more distant gravitational-wave events.

The goal for the next generation of gravitational-wave detectors is to achieve about 10 times the sensitivity of today’s instruments,” said Jonathan Richardson, an associate professor of physics and astronomy at UC Riverside who led the study. “One of the key obstacles to achieving that is reducing the fundamental quantum-mechanical noise that limits the precision of the measurements.”

From quantum error correction to emergent gravity: Probing holographic universes at QLab

One of the deepest ambitions in modern physics is understanding how the fabric of space and time could emerge from fundamental quantum degrees of freedom to establish a quantum theory of gravity.

In the new paper, “Observation of gravity-like signatures in holographic codes on a quantum computer,” posted to the arXiv preprint server, researchers from the National Quantum Laboratory (QLab@UMD), the Duke Quantum Center, the Virginia Tech Center for Quantum Information Science and Engineering, Caltech’s Institute for Quantum Information and Matter, IonQ and BlueQubit have successfully simulated toy models of quantum gravity according to the AdS/CFT correspondence. The team, led by Crystal Noel and Charles Cao, includes quantum-computation pioneers John Preskill and Christopher Monroe.

Using the IonQ Forte ion-trap quantum computer, the study implements the intriguing HaPPY quantum error-correction code, which forms a bridge between quantum computing and quantum gravity. This code simulates a highly simplified model of a universe with a negative cosmological constant that features a so-called bulk-boundary correspondence, in which the properties of a higher-dimensional gravitational universe (bulk) are completely determined by a lower-dimensional quantum system without gravity living on the boundary. The team successfully demonstrated fundamental entanglement properties of these systems.

Frozen fiber couples light and sound 1,000 times more strongly than standard glass fibers

Researchers have developed a new type of optical fiber by freezing a glass capillary filled with liquid. It guides light and sound waves simultaneously and enables highly efficient coupling between them. The high coupling strength lowers the energy consumption of photonic neuromorphic computing schemes and quantum signal processing applications by several orders of magnitude.

When volcanoes erupt, one can observe streams of liquid lava cool and solidify into rock formations at the bottoms of volcanoes. The same physical process—a liquid changing into a solid phase upon cooling—can be observed when lakes start freezing during cold winters. These phase changes always come with changes in the physical properties of the material, such as the density or refractive index that govern how sound and light move through it.

This fundamental physical process is also used during the melting of glass preforms to loosen their structure while drawing optical fiber. These fibers then guide light through their cores, allowing the transmission of information via light very quickly over long distances, which is why they are widely used for telecommunications applications.

Quantum sensing microscope illuminates transistor design

Artificial intelligence faces an energy crisis stemming from a physical traffic jam inside modern computer chips. Processors must continually shuffle data, such as the billions of parameters in complex models, between separate computing and memory nodes. This traffic jam, known as the “von Neumann bottleneck,” hinders the speed and energy efficiency of advanced processors.

To tackle this problem, scientists are developing spintronics, which leverages the electron’s “spin,” or intrinsic magnetic orientation, for more efficient devices. A long-sought milestone in this field is a single device, known as a “spin transistor,” that combines a magnetic bit with a semiconducting switch, allowing it to compute and store data simultaneously.

“The major challenge is understanding how magnetism and electrical current interact in nanoscale devices,” said Boston College physics professor Brian Zhou, whose group led the study. “We developed a single-spin quantum microscope to observe magnetic states inside atomically thin devices as they actively process electrical information.”

Quantum entanglement without transport: Leaky qubits offer route around noisy channels

The inevitable leakage of energy and information from a quantum system into its surrounding environment is the enemy of quantum technology. Now, researchers have demonstrated that it can be exploited to generate entanglement—the “resource” that quantum technologies use to perform tasks inaccessible to standard classical technologies.

A collaboration between physicists at the University of Illinois Urbana-Champaign and the University of Chicago has realized a theoretical prediction in which an externally driven quantum system achieves entanglement through dissipation. While the original prediction relies on highly idealized settings, the researchers developed a new technique called synthetic squeezing to realize the phenomenon in a laboratory setting with a pair of superconducting qubits.

Moreover, the generated entanglement is in a steady state, meaning that, in principle, it can be maintained indefinitely over arbitrarily large distances. The researchers believe that this technique holds promise as a more robust and reliable alternative to current methods of entanglement generation.

How quantum circuits based on neutral atoms could find and fix errors

Quantum computers, devices that process information by leveraging the laws of quantum mechanics, have been found to outperform classical computers in some advanced tasks. Instead of storing information in the form of classical binary bits (i.e., 0 or 1), quantum computers rely on quantum bits (i.e., qubits), which can also exist in combinations of 0 and 1 states.

Despite their potential, quantum computers are known to be highly prone to errors. This is because qubits are very sensitive to heat, magnetic fields and other changes in their surroundings, which can disrupt the delicate quantum states they rely on to store and process data.

Researchers at Princeton University recently introduced a new approach for developing quantum computers that make fewer errors and whose errors are easier to detect and correct.

A scheme to verify gates of a quantum computer without examining devices

Quantum computers, systems that process information using the principles of quantum mechanics, could solve some problems that cannot be tackled by the classical computers currently used worldwide. Despite their potential, verifying that these computers are working correctly and can reliably perform computations remains challenging.

Shubhayan Sarkar, a researcher at the University of Gdansk, recently introduced a new scheme for certifying that quantum chips (unitary gates) in a quantum computer are operating correctly without relying on assumptions about their internal components. This scheme, introduced in a paper published in Physical Review Letters, uses an approach referred to as almost device-independent (DI) certification.

“Consider the computer you are using right now,” Sarkar told Phys.org. “If it provides the answer to a mathematical problem, how do you know that the computation is correct? In practice, we rarely verify every calculation ourselves.

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