Quantum Computing
Learn about quantum algorithms, quantum information theory, and quantum computing applications
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Sat, Nov 15
52 items found
Tuning the Critical Current in Toroidal Superfluids via Controllable Impurities
We combine numerical and experimental approaches to study how impurities affect the maximum superflow in an annular Bose-Einstein condensate. By tuning the impurity density, we achieve precise control over the stability of persistent currents which increases with the impurity number. In the unstable regime, the complex vortex motion within the impurity landscape, characterized by pinning and unpinning events, governs the timescale of the current decay and its final value. Our work establishes atomic superfluids as a pristine platform for exploring universal mechanisms of superflow stabilization and decay, paving the way for atomtronic quantum technologies.
Quantum Computational Structure of $SU(N)$ Scattering
We study scattering of particles which obey an $SU(N)$ global symmetry through the lens of quantum computation and quantum algorithms. We show that for scattering between particles which transform in the fundamental or anti-fundamental representations, i.e. qudits, all 2-2 scattering amplitudes can be constructed from only three quantum gates. Further, for any $N$, all 2-2 scattering channels are shown to emerge from the span of a $\mathbb{Z}_{2}$ algebra, suggesting that scattering in this context is fundamentally governed by the action of ``bit flips'' on the internal quantum numbers. We frame these findings in terms of quantum algorithms constructed from Linear Combinations of Unitaries and block encoding.
Observation and Manipulation of Optical Parametric Down-Conversion in the Langevin Regime
Quantum fluctuation plays a key role in the parametric down-conversion in the Langevin regime. In this paper, we report the experimental realization of optical parametric down-conversion in the Langevin regime on a chip. By precisely controlling the loss inherently tied to fluctuation, we observe the asymmetric Hong-Ou-Mandel dip - a hallmark of quantum fluctuation in the fluctuation-driven PDC, and the fluctuation-induced compression of single photons by nearly one order of magnitude. These findings pave the way for the manipulation of quantum fluctuation, quantum states, and system-reservoir interaction.
Crossing Symmetry and Entanglement
We study the interplay between crossing symmetry and entanglement in $2 \to 2$ scattering within local quantum field theories that possess an $SU(N)$ global symmetry. In particular, we recast scattering amplitudes of fixed helicity as quantum operations on the Hilbert space of internal quantum numbers, where the external states play the role of qudits. The entire space of $SU(N)$-invariant scattering operators between qudits is spanned by a minimal set of three quantum gates. Recoupling relations among quantum gates are shown to follow directly from the crossing properties of the underlying amplitudes and reveal that entanglement generated from separable states in one channel is necessarily intertwined with another. Consequently, we argue any interacting quantum field theory that realizes an $SU(N)$ global symmetry must generate entanglement in at least one scattering channel.
Finite-size quantum key distribution rates from Rényi entropies using conic optimization
Finite-size general security proofs for quantum key distribution based on Rényi entropies have recently been introduced. These approaches are more flexible and provide tighter bounds on the secret key rate than traditional formulations based on the von Neumann entropy. However, deploying them requires minimizing the conditional Rényi entropy, a difficult optimization problem that has hitherto been tackled using ad-hoc techniques based on the Frank-Wolfe algorithm, which are unstable and can only handle particular cases. In this work, we introduce a method based on non-symmetric conic optimization for solving this problem. Our technique is fast, reliable, and completely general. We illustrate its performance on several protocols, whose results represent an improvement over the state of the art.
Quantum Algorithms for Computing Maximal Quantum $f$-divergence and Kubo-Ando means
The development of quantum computation has resulted in many quantum algorithms for a wide array of tasks. Recently, there is a growing interest in using quantum computing techniques to estimate or compute quantum information-theoretic quantities such as Renyi entropy, Von Neumann entropy, matrix means, etc. Motivated by these results, we present quantum algorithms for computing the maximal quantum $f$-divergences and the operator-theoretic matrix Kubo--Ando means. Both of them involve Renyi entropies, matrix means as special cases, thus implying the universality of our framework.
Supernematic
Quantum theory of geometrically frustrated systems is usually approached as a gauge theory where the local conservation law becomes the Gauss law. Here we show that it can do something fundamentally different: enforce a global conserved quantity via a non-perturbative tiling invariant, rigorously linking microscopic geometry to a new macroscopically phase-coherent state. In a frustrated bosonic model on the honeycomb lattice in the cluster-charging regime at fractional filling, this mechanism protects a conserved global quantum number, the sublattice polarization $\tilde{N} = N_A - N_B$. Quantum fluctuation drives the spontaneous symmetry breaking of this global U(1) symmetry to result in a supernematic (SN) phase -- an incompressible yet phase-coherent quantum state that breaks rotational symmetry without forming a superfluid or realizing topological order. This establishes a route to a novel quantum many-body state driven by combinatorial constraints.
Shallow IQP Circuits Generate Graphs with up to 128 Nodes, Maintaining Accuracy to 0.05 Total Variation
Researchers demonstrate that compact quantum circuits, utilising readily available quantum hardware, successfully learn and reproduce the structural characteristics of complex networks, even without error correction, establishing a promising pathway for generative modelling in the emerging field of quantum computing.
Quantum Tensor Representation Via Circuit Partitioning Enables Algorithms on Noisy QPU Hardware
Researchers have developed a new method, shardQ, that significantly improves the performance of quantum computations by intelligently dividing and reconnecting circuits, demonstrably balancing speed and accuracy even on current, imperfect quantum hardware.
Federated Quantum Kernel Learning Enables Privacy-Preserving Anomaly Detection in Multivariate IoT Time-Series
A new framework enables privacy-preserving anomaly detection in complex industrial sensor networks by combining local data analysis with a central system that learns from compressed summaries, significantly improving accuracy and efficiency compared to traditional methods.
Trustworthy Quantum Machine Learning Roadmap Enables Reliability, Robustness, and Security in the NISQ Era
This research establishes a comprehensive framework for trustworthy quantum machine learning, integrating methods to quantify uncertainty, ensure robustness against attacks, and preserve privacy, thereby paving the way for reliable quantum AI systems.
Cdse/zns, MOF Quantum Dot Composites: Theoretical Framework Calculates Third-Order Nonlinear Susceptibility
Researchers have established a predictive model, grounded in fundamental physical principles, to accurately determine and optimise the nonlinear optical properties of semiconductor nanocrystals embedded within supporting materials, offering a pathway to design materials with enhanced light-manipulating capabilities.
Secure PAC Learning Achieves, PAC Learnability with Quantum Data-Path Admissibility
Researchers have established a new theory of machine learning where guaranteed learning success directly depends on a quantifiable information advantage, offering a fundamentally new approach to building certified, reliable algorithms.
Nishimori Multicriticality Study Achieves Precise Critical Point Extraction at 0.46, Using Information Measures and up to Disorder Realizations
Researchers precisely pinpoint the threshold at which quantum error correction fails, using a novel information-based approach and detailed analysis of disordered magnetic systems to demonstrate robust agreement with established theoretical predictions.
Frequency Shifts Reveal Ground State Squeezing and Entanglement in Coupled Harmonic Oscillators
Researchers demonstrate that even coupled oscillators at their lowest energy state exhibit detectable signatures of quantum entanglement through measurable shifts in their characteristic frequencies, revealing a pathway to enhance precision measurements without requiring conventionally squeezed light.
Cuprate Twistronics Enables Quantum Hardware Via Nanoscale Engineering of Superconducting Films
Researchers are precisely manipulating layers of complex materials, including cuprate superconductors, to create and study novel electronic states with the potential to advance future technologies.
Quantum Chaos Boosts Circuit Design Quality Via Subsystem Measurement and Early-Time Dynamics
Researchers demonstrate that measuring part of a complex quantum system can surprisingly enhance its randomness, even when generated by chaotic processes, and establish a fundamental limit to how much randomness can be lost through such measurement.
Quantum Variational Algorithms Overcome Noise with Population Mean Tracking for Reliable Optimization
Researchers demonstrate that adaptive optimisation techniques, particularly those inspired by evolutionary strategies, reliably overcome noise-induced errors in quantum calculations, enabling more accurate simulations of complex molecular systems and materials.
Compact Dual-Beam Zeeman Slower Captures Increased Rubidium Flux, Eliminates Window Contamination Within 44cm
A newly designed compact Zeeman slower, utilising two laser beams and a capillary array, significantly enhances the capture of cold atoms, such as rubidium and ytterbium, while virtually eliminating contamination that limits the lifespan of devices used in precision measurement and quantum technologies.
Quantum Metrology in Double-Morse Potential Achieves Enhanced Estimation with Rising Non-Classicality
Researchers demonstrate that a specifically shaped energy landscape, the double-Morse potential, provides a controllable source of non-classical light that becomes increasingly useful for advanced information processing as its asymmetry is increased.