Key Physical Processes in Quantum Systems

Chinese Researchers Slow Quantum Chaos Using 78-Qubit Processor Scientists at the Chinese Academy of Sciences have used their 78-qubit superconducting processor, Chuang-tzu 2.0, to directly observe and control a key transitional phenomenon in quantum systems known as prethermalisation. The work offers a new pathway to manage quantum decoherence—the core obstacle to scalable quantum computing. The Core Challenge In quantum systems, stored information naturally disperses through a process called decoherence. Once decoherence dominates, qubits lose their usable state information, undermining computational reliability. Modeling this process on classical computers is computationally infeasible for systems approaching 100 qubits due to the exponential growth of state space. Using Quantum Hardware as a Physics Laboratory Instead of simulating decoherence classically, the team used their quantum processor itself as a physical simulator. For large quantum systems, the processor effectively becomes an experimental platform to observe complex dynamical laws directly—analogous to a wind tunnel for aerodynamics. Discovery of the Prethermalisation Plateau The researchers observed an intermediate stage before full thermalisation: • A temporary plateau where quantum chaos is suppressed. • Information remains partially localized rather than fully scrambled. • Decoherence progression slows before complexity rapidly increases. This “prethermalisation plateau” creates a controllable time window during which quantum information can be utilized before it dissipates irreversibly. Control and Tunability Critically, the team demonstrated that this stage is not merely observable but adjustable: • Tailored control sequences altered both the duration and structure of the plateau. • Researchers were able to extend or shorten the prethermalisation phase. • This suggests active engineering of decoherence timelines may be feasible. Strategic Implications The findings matter for three reasons: Extending Coherence Windows Controlled prethermalisation could lengthen usable qubit lifetimes. Improving Error Correction Understanding how complexity spreads may inform better quantum error-correction architectures. Hardware as Fundamental Science Tool The experiment highlights a broader shift: quantum processors are becoming instruments for probing physics beyond classical computational limits. Perspective If decoherence is the central scaling barrier in superconducting quantum computing, then controllable prethermalisation introduces a new lever. Rather than merely fighting noise, engineers may be able to shape the temporal structure of quantum chaos itself. In a competitive global landscape, advances like this underscore how quantum hardware is evolving from prototype processors into platforms for exploring—and potentially mastering—the dynamics that limit quantum advantage.

As a physicist, I’m constantly amazed by the power of the Josephson Junction (JJ). This tiny component is the workhorse of superconducting qubit circuits and plays a critical role in many other parts of the cryogenic setup in quantum processors. So, what exactly is a Josephson Junction? A Josephson Junction is a quantum mechanical system consisting of two superconductors separated by a thin insulating barrier. This structure allows for the tunneling of Cooper pairs (pairs of electrons bound together at low temperatures), leading to the Josephson effect—where a supercurrent can flow across the barrier even without any applied voltage. Why is such a system crucial for superconducting qubits? Josephson Junctions are the core of superconducting qubit circuits. They introduce the crucial nonlinearity that distinguishes two discrete energy levels from higher states, allowing the circuit to function as a two-level quantum system—what we call a qubit. But their role extends far beyond qubits. Josephson Junctions are key components in parametric amplifiers, which amplify signals with minimal noise—crucial for qubit readout. They’re also at the heart of Single-Flux Quantum (SFQ) technology, which can generate control signals for qubits at cryogenic temperatures. Additionally, JJs are now being used to create non-reciprocal devices like on-chip circulators. Excitingly, JJs are used and explored beyond quantum processors. For instance, imec is developing JJ-FETs, a next-generation transistor technology that could revolutionize classical computing as well. What's your favourite application of the Josephson Junction ?

NUCLEATION OF SOLITONIC EXCITATIONS ENABLE THE FABRICATION OF ATOMTRONIC CIRCUITS The Josephson effect is one of the cornerstone phenomena of quantum physics, enabling dissipation‑free electrical currents to flow across a thin barrier between two superconductors. This remarkable behavior—arising from the phase coherence of Cooper‑pair wavefunctions—forms the foundation of superconducting quantum interference devices (SQUIDs), voltage standards, and many of today’s superconducting qubits. When a microwave field is applied across a Josephson junction, the system develops a staircase‑like current–voltage response known as Shapiro steps, a signature of photon‑assisted tunneling that depends only on fundamental constants. In recent years, physicists have discovered that the Josephson effect is not limited to electronic superconductors. It can also be realized in ultracold quantum gases, where atoms rather than electrons tunnel across a barrier. This capability has opened the door to atomtronics—a rapidly growing field in which ultracold atoms are used to build analogs of electronic circuits, offering unprecedented control over quantum transport and coherence. In a new experimental breakthrough, researchers have demonstrated the emergence of Shapiro steps in an atomic Josephson junction, confirming that the defining features of the Josephson effect persist even when electrons are replaced by neutral atoms. By separating two Bose–Einstein condensates with a narrow optical barrier and periodically modulating the barrier’s position, the team recreated the conditions of a microwave‑driven superconducting junction. Crucially, the experiment provided microscopic insight into the dynamics underlying these steps. By imaging the atomic density in real time, the researchers observed the emission of phonons and the formation of solitonic excitations—localized density depletions that propagate away from the barrier. These solitons represent a new window into the dissipative and collective processes that accompany Josephson transport, processes that are extremely difficult to access in solid‑state systems. Because ultracold atoms evolve on much longer time and length scales than electrons in superconductors, they allow direct visualization of phenomena that are otherwise hidden. Below the critical current, only a single phononic wave is emitted. Above the critical current, the system enters the ac Josephson regime, where the moving barrier leaves behind a persistent density depletion—a soliton—revealing the onset of nonlinear dynamics. This work not only confirms the universality of Shapiro steps across fundamentally different physical platforms, but also establishes a powerful method for probing the equation of state of strongly correlated superfluids. The quantized relationship between chemical potential and driving frequency provides a tunable, measurable link between microscopic excitations and macroscopic transport. # https://lnkd.in/ebuXfay5

Scientists have discovered that quantum processes previously thought to be instantaneous actually take measurable time. Researchers at TU Wien, led by Professor Joachim Burgdörfer and Professor Iva Březinová, have calculated that quantum entanglement - where particles become connected regardless of distance - develops over approximately 232 attoseconds (a quintillionth of a second). Their study, published in Physical Review Letters, used simulations of intense laser pulses striking atoms to show how one electron gets ejected while another moves to a higher orbital. The timing of the first electron's departure directly correlates with the state of the electron left behind, creating quantum entanglement. This process happens as the departing electron "spills out" of the atom like a wave, taking measurable time rather than occurring instantaneously. The researchers are now collaborating with experimental teams to verify these ultrahigh-speed entanglements in laboratory settings. 💡 Why It's Important - This discovery suggests that within quantum mechanics, even the most rapid quantum phenomena unfold over definite timeframes. By establishing that entanglement has a "birth time," scientists gain new insights into cause-and-effect relationships in the quantum realm. The ability to measure events at attosecond scales - where light travels just the width of a human hair - represents a remarkable achievement in precision quantum research. This research suggests that the quantum world, while bizarre, may still operate within the framework of time. What once seemed like magical instantaneous connections between particles may actually unfold through measurable processes. #RMScienceTechInvest

Hey You! Got a quick Attosecond? For decades, we’ve talked about quantum entanglement as if it “just happens.” Now we’re starting to put a clock on how it forms. A team led by TU Wien (Vienna University of Technology), working with collaborators in China, used ultrafast simulations and a proposed two-laser measurement protocol to resolve the temporal structure of an event that’s usually treated as instantaneous. The mind-bender is that the departing electron doesn’t have a single, well-defined “birth time.” Instead, that timing is quantum-linked to the energy state of the electron left behind—with an average offset on the order of ~232 attoseconds. That’s 0.000000000000000232 seconds. To give you some perspective - a blink of an eye (~0.1 seconds) is about 430 trillion times longer than 232 attoseconds Here’s the physical picture they analyze: Start with an atom that has two electrons. Hit it with an extremely intense, high-frequency laser pulse. One electron is ripped out (ionized) and rushes away. The second electron remains bound, but can be kicked into a different (higher-energy) state. At that point, the system is no longer well-described as “electron A plus electron B.” The key outcome is that the two electrons become one joint quantum object—their properties are correlated in a way that can’t be reduced to independent “facts” about each electron. The most interesting twist is what becomes entangled. In their analysis, the “birth time” of the escaping electron—the moment it truly “left” the atom—is not a single, definite timestamp. Instead, it’s in a quantum superposition of different departure times, and those possible times are linked to the energy state of the electron left behind. Practically, that means: If the remaining electron ends up in a higher-energy state, the departing electron was more likely ejected earlier. If the remaining electron ends up in a lower-energy state, the departing electron was more likely ejected later—with an average offset on the order of ~232 attoseconds (232 × 10⁻¹⁸ seconds). That’s the real substance behind the popular phrasing “entanglement speed.” The point is not that entanglement is slow—it’s that even “instantaneous” quantum events can have measurable internal timing when you probe them on attosecond scales. Why it matters (beyond the headline): If you can resolve when and how correlations form—rather than only confirming they exist after the fact—you get leverage. You move from “entanglement is a weird thing we observe” to “entanglement is a dynamical process we can potentially engineer, shape, and control.” https://lnkd.in/gqPn34FA #QuantumEntanglement #QuantumPhysics #Attosecond #UltrafastScience #LaserPhysics #ElectronDynamics #AtomicPhysics #QuantumInformation #QuantumResearch #Physics