96 papers in the last 30 days, 5 in the 30 days before (+1820%).
Helper-assisted quantum sensing with low dressed-state leakage (opens in a new tab)
arXiv - Quantum physics
We study a two-qubit sensing protocol in which only a helper qubit is read out. Calibrated loading and unloading encode a transverse signal in the helper's phase, keep leakage out of a selected dressed-state band small, and return the sensor close to its idle ground state. We derive an information bound for a single sensor whose excitation stays below a prescribed budget, and simulate repeated ope
Engineered Learning Problems on Noisy Quantum Processors (opens in a new tab)
arXiv - Quantum physics
Despite quantum machine learning being an active topic of research, demonstrations of algorithms run on quantum hardware beating classical methods remain rare. In this work, we demonstrate a significant performance gap using a projected quantum kernel for $n=15,30$ and $45$ qubits over classical methods on an engineered classification problem, and show reproducibility of the results over different
Finite-resource cooling of qudits beyond thermodynamic length (opens in a new tab)
arXiv - Quantum physics
Cooling a quantum system with $N$ thermal machines costs more than Landauer's bound. For swap-based collision models the excess is set by thermodynamic length, which is optimal for qubits and was suggested by numerics to be optimal in general. We show that for qudits, permutations of energy eigenstates that use several resonant transitions at once do better for every spectrum, reducing the excess
Quantum Bernstein--Kolmogorov--Arnold approximation (opens in a new tab)
arXiv - Quantum physics
This paper addresses the expressivity and representation gap in Quantum Neural Networks by establishing a quantum analogue of the classical Kolmogorov--Arnold representation theorem. We propose a constructive approximation framework over fixed input coherent states, where the dependence of the function argument is embedded entirely in coordinate qubits, while the target function dictates a single
Symmetries and model reduction in a $\cos 2\varphi$ transmon qubit (opens in a new tab)
arXiv - Quantum physics
Engineered symmetries in superconducting circuits can protect quantum information; much like selection rules in atomic physics, they forbid transitions between the qubit states. Protected circuits, however, combine several loops and islands and host multiple nonlinearly coupled modes, calling for reduced low-energy models that inherit the circuit symmetries and make the protection manifest. We dev
Clifford synthesis is NP-complete (opens in a new tab)
arXiv - Quantum physics
We show that the problem of synthesizing a quantum circuit for a given Clifford operator using at most a specified amount of resources is NP-complete for several resource models of practical interest. Specifically, we study synthesis of a given Clifford operator using single-qubit Clifford gates and two-qubit Clifford gates, with full qubit connectivity and no additional ancilla qubits. With singl
Topologically Protected Edge States in a Single Flux Qubit (opens in a new tab)
arXiv - Quantum physics
We show that topological edge states can be realized in a simple superconducting circuit composed of an inductively shunted flux qubit. The Josephson potential of that qubit forms a honeycomb lattice similar to the case of graphene. The additional shunting element produces a quartic potential along one flux direction, which effectively creates a boundary in flux space. We map analytically the low-
Electronic-Structure-Informed Many-Body Encoding for Quantum Machine Learning (opens in a new tab)
arXiv - Quantum physics
Data encoding is a central challenge in quantum machine learning (QML), as it determines how classical information is mapped onto quantum states and influences the expressive power and efficiency of parameterized quantum circuits. Here, we introduce a physics-informed quantum encoding strategy that exploits the intrinsic many-body structure of electronic systems to establish a direct correspondenc
arXiv - Quantum physics
Sample-based quantum diagonalization has been used as an impurity solver in density matrix embedding theory (DMET), but always with fixed-form circuits and without comparison to classical selection at the same subspace size. We introduce GENIE, a DMET impurity solver in which a generative transformer learns the sampling circuit, trained on the quantum-selected configuration interaction energy. On
Bounding Fidelity of Non-Stabilizer States from Local Pauli Measurements (opens in a new tab)
arXiv - Quantum physics
Nonstabilizerness, commonly referred to as magic, is essential for universal quantum computation. Yet, for pure $n$-qubit states this property is directly linked to the hardness of direct fidelity estimation. We propose a scheme to bound the fidelity on non-stabilizer states by choosing operators with low measurement overhead and using parallel local Pauli measurements to estimate compatible obser
arXiv - Quantum physics
We introduce FaultScope, a classical simulator for quantum error correction circuits, implemented in Rust with a Python interface. FaultScope estimates logical error rates and their derivatives with respect to component error rates from the same sampled and decoded shots, without modifying or differentiating through the decoder. These derivatives enable error attribution to individual noisy compon
arXiv - Quantum physics
Quantum processors are now used as feature generators for classical models on tabular data. A circuit encodes each record, the device returns expectation values, and a classical model learns from them. A recent report claimed large gains from such features, gains that appeared only on noisy hardware. These claims are hard to check, because a quantum device is not a static function. Its state chang
arXiv - Quantum physics
Scaling silicon spin qubits to fault-tolerant processors requires semiconductor foundry integration, yet it remains unclear how industrial fabrication and dense device integration affect qubit control and noise. Here we study ${}^{28}\mathrm{Si}/\mathrm{SiGe}$ electron spin-1/2 qubits fabricated using Intel's industry-compatible 300 mm process and incorporating micromagnets for electrically driven
arXiv - AI / ML / NLP
Quantum Neural Networks (QNNs) offer a framework for learning functions from classical data, but their expressive power depends critically on how inputs are encoded into quantum states. Angle encoding can require resources that scale with the number of features, whereas amplitude encoding represents $d$ features using only $\mathcal{O}(\log_2 d)$ qubits. This compactness comes at a representationa
arXiv - AI / ML / NLP
A coherent sum of quantum circuits introduces interference that can alter the training signal. We distinguish a single linear combination of unitaries (LCU) from a circuit that repeatedly alternates branch operations and ancilla mixing. For a single-pass LCU, independent branches with zero matrix means cannot erase the differentiated branch's gradient variance: the total variance is at least the b
arXiv - Quantum physics
Stochastic resetting drives quantum systems into nonequilibrium stationary states unreachable under uninterrupted unitary evolution, and their entanglement depends on whether the reset history is resolved or averaged over. We study this interplay in the transverse-field Ising chain, deriving closed-form results for two qubits and evaluating chains of up to 12 qubits exactly. In the two-qubit syste
Lower Bound for Region of Non-Distillable Magic States (opens in a new tab)
arXiv - Quantum physics
Magic states are a leading proposal for realizing fault-tolerant and universal quantum computation. At the present moment, much of the theory of magic states is not understood. Even simple questions such as what single qubit states have magic remain open. In Campbell and Browne's seminal paper on bound magic states, they prove the existence of states outside of the stabilizer octahedron which cann
arXiv - Quantum physics
We provide a detailed resource estimate of the state-of-the-art sum-of-squares block encoding algorithm for electronic structure Hamiltonians of Low et al. on superconducting cat qubits. To achieve this, we present compilations with closed-form costs of the dominant subroutines such as skew-tree Qrom, a Swap network and a Phaseup for both a repetition-cat and an LDPC-cat architecture. Our compilat
arXiv - Quantum physics
This paper proposes a VLSI-like design and verification flow for quantum circuit implementation, covering four levels: behavioral modeling, register-transfer level (RTL), gate level, and full-circuit integration with quantum algorithms. Using quantum Monte Carlo methods for pi estimation as a case study, the proposed flow provides a systematic path from initial specifications to large-scale quantu
arXiv - Quantum physics
This review aims to provide researchers, experimentalists, and quantum engineers with an updated and technically grounded perspective on the implementation of quantum gates in superconducting NISQ devices. The goal is to establish a comprehensive bridge between theoretical quantum circuit synthesis and its practical, experimental implementation, focusing on superconducting quantum technologies. We
arXiv - Quantum physics
Phonon bursts from ionizing radiation cause correlated errors in superconducting quantum processors. We study prescribed nonequilibrium phonon pulses in a Majorana qubit formed by two $2\,\mu\mathrm{m}$ proximitized nanowires. Combining the lattice Lutchyn--Oreg model, microscopic electron--phonon coupling, and parity-resolved many-body dynamics, we track excitation, relaxation, and logical cohere
Digital-Analog Quantum Neural Network with Long-Range Interactions (opens in a new tab)
arXiv - Quantum physics
Protocols combining single-qubit digital operations with analog quantum evolutions bypass large numbers of two-qubit entangling gates, offering a promising approach to variational algorithms and hybrid quantum simulation. Focusing on the digital-analog quantum neural network (DA-QNN) as a representative framework, this work demonstrates that incorporating long-range interactions enhances the effic
arXiv - Quantum physics
We present an end-to-end resource estimation of Shor's algorithm on superconducting cat qubits, from its mathematical description to the allocation and scheduling of physical qubits on a chip layout. We review modern versions of Shor's algorithm for RSA, ECDLP and FFDLP, and make their logical circuits and trade-offs explicit. We compile the dominant subroutines down to physical-qubit operations o
arXiv - Quantum physics
The quantum approximate optimization algorithm (QAOA) is a paradigmatic variational quantum algorithm for combinatorial optimization problems, yet on current quantum devices the available qubit count and achievable circuit depth remain the main bottlenecks to its practical application. Divide-and-merge reduces the number of variables encoded in a single quantum circuit, while contraction based on
Einstein Metrics and Quantum Control on Symmetric Tensor Product Quotients (opens in a new tab)
arXiv - Quantum physics
Let $M_n=(\mathrm{PU}(2)^n\rtimes S_n)\backslash\mathrm{PU}(2^n)$ be the space of projective $n$-qubit unitaries modulo local unitaries and permutations of the qubits. We prove that for all sufficiently large $n$ the manifold $M_n$ carries exactly two $\mathrm{PU}(2^n)$-invariant Einstein metrics up to scaling. Both Einstein metrics have uniformly bounded diameter after normalizing two-qubit costs
arXiv - Quantum physics
Quantum systems are intrinsically fragile and highly vulnerable to environmental noise, making the preservation of quantum states one of the fundamental challenges in realizing practical quantum technologies. We propose two noise-agnostic quantum state protection protocols based on a collisional model. The first protocol preserves quantum states of qubits without requiring complete prior knowledge
The Geometry of Quantum Teleportation in Phase Space (opens in a new tab)
arXiv - Quantum physics
We formulate the standard quantum teleportation protocol within the framework of deformation quantization, employing the Stratonovich--Weyl (SW) correspondence and the associated star product on the coadjoint orbits of $SU(2)$. Each qubit is represented by a spherical phase space $S^2$ endowed with the Kirillov--Kostant--Souriau (KKS) symplectic structure. Within this setting, we explicitly constr
arXiv - Quantum physics
Reconfigurable neutral-atom processors couple gate scheduling, atom placement, and parallel atom transport, so compiler decisions jointly determine physical execution costs. Evaluating these compilers requires attainable resource references and a way to trace excess costs to their causes. We present NAKO, a benchmarking framework that parameterizes circuits by qubit count, logical depth, and reque
High-Threshold Fusion-Based Quantum Computation with Optical Hybrid Qubits (opens in a new tab)
arXiv - Quantum physics
Hybrid discrete- and continuous-variable (DV-CV) encodings have been developed to overcome operational drawbacks of each individual encoding, while fusion-based quantum computation (FBQC) has emerged to address the practical challenges of scalability toward fault-tolerant photonic quantum computation. Here we introduce hybrid FBQC using small optical DV-CV hybrid resource states connected through
Three-dimensional QCA that are not stably circuits (opens in a new tab)
arXiv - Quantum physics
We prove that the three-dimensional chiral $\Z_p$ Clifford quantum cellular automata of Haah and of Sun--Yang--Wang--Tantivasadakarn--Chen are, for every odd prime $p$, not finite-depth quantum circuits, even after tensoring with arbitrary ancillary degrees of freedom and composing with translations. Previously such statements were known only inside the Clifford category. As a consequence, the gro