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Improved Quantum Query Complexity on Easier Inputs Quantum (IF 6.4) Pub Date : 2024-04-08 Noel T. Anderson, Jay-U Chung, Shelby Kimmel, Da-Yeon Koh, Xiaohan Ye
Quantum span program algorithms for function evaluation sometimes have reduced query complexity when promised that the input has a certain structure. We design a modified span program algorithm to show these improvements persist even without a promise ahead of time, and we extend this approach to the more general problem of state conversion. As an application, we prove exponential and superpolynomial
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Inplace Access to the Surface Code Y Basis Quantum (IF 6.4) Pub Date : 2024-04-08 Craig Gidney
In this paper, I cut the cost of Y basis measurement and initialization in the surface code by nearly an order of magnitude. Fusing twist defects diagonally across the surface code patch reaches the Y basis in $\lfloor d/2 \rfloor + 2$ rounds, without leaving the bounding box of the patch and without reducing the code distance. I use Monte Carlo sampling to benchmark the performance of the construction
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Efficient solution of the non-unitary time-dependent Schrodinger equation on a quantum computer with complex absorbing potential Quantum (IF 6.4) Pub Date : 2024-04-08 Mariane Mangin-Brinet, Jing Zhang, Denis Lacroix, Edgar Andres Ruiz Guzman
We explore the possibility of adding complex absorbing potential at the boundaries when solving the one-dimensional real-time Schrödinger evolution on a grid using a quantum computer with a fully quantum algorithm described on a $n$ qubit register. Due to the complex potential, the evolution mixes real- and imaginary-time propagation and the wave function can potentially be continuously absorbed during
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Quantum advantage in temporally flat measurement-based quantum computation Quantum (IF 6.4) Pub Date : 2024-04-09 Michael de Oliveira, Luís S. Barbosa, Ernesto F. Galvão
Several classes of quantum circuits have been shown to provide a quantum computational advantage under certain assumptions. The study of ever more restricted classes of quantum circuits capable of quantum advantage is motivated by possible simplifications in experimental demonstrations. In this paper we study the efficiency of measurement-based quantum computation with a completely flat temporal ordering
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Optimizing Variational Quantum Algorithms with qBang: Efficiently Interweaving Metric and Momentum to Navigate Flat Energy Landscapes Quantum (IF 6.4) Pub Date : 2024-04-09 David Fitzek, Robert S. Jonsson, Werner Dobrautz, Christian Schäfer
Variational quantum algorithms (VQAs) represent a promising approach to utilizing current quantum computing infrastructures. VQAs are based on a parameterized quantum circuit optimized in a closed loop via a classical algorithm. This hybrid approach reduces the quantum processing unit load but comes at the cost of a classical optimization that can feature a flat energy landscape. Existing optimization
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Efficient Computation of the Quantum Rate-Distortion Function Quantum (IF 6.4) Pub Date : 2024-04-09 Kerry He, James Saunderson, Hamza Fawzi
The quantum rate-distortion function plays a fundamental role in quantum information theory, however there is currently no practical algorithm which can efficiently compute this function to high accuracy for moderate channel dimensions. In this paper, we show how symmetry reduction can significantly simplify common instances of the entanglement-assisted quantum rate-distortion problems. This allows
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Classical analogue of quantum superdense coding and communication advantage of a single quantum system Quantum (IF 6.4) Pub Date : 2024-04-09 Ram Krishna Patra, Sahil Gopalkrishna Naik, Edwin Peter Lobo, Samrat Sen, Tamal Guha, Some Sankar Bhattacharya, Mir Alimuddin, Manik Banik
We analyze utility of communication channels in absence of any short of quantum or classical correlation shared between the sender and the receiver. To this aim, we propose a class of two-party communication games, and show that the games cannot be won given a noiseless $1$-bit classical channel from the sender to the receiver. Interestingly, the goal can be perfectly achieved if the channel is assisted
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Double-bracket quantum algorithms for diagonalization Quantum (IF 6.4) Pub Date : 2024-04-09 Marek Gluza
This work proposes double-bracket iterations as a framework for obtaining diagonalizing quantum circuits. Their implementation on a quantum computer consists of interlacing evolutions generated by the input Hamiltonian with diagonal evolutions which can be chosen variationally. No qubit overheads or controlled-unitary operations are needed but the method is recursive which makes the circuit depth grow
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From Non-Markovian Dissipation to Spatiotemporal Control of Quantum Nanodevices Quantum (IF 6.4) Pub Date : 2024-04-03 Thibaut Lacroix, Brendon W. Lovett, Alex W. Chin
Nanodevices exploiting quantum effects are critically important elements of future quantum technologies (QT), but their real-world performance is strongly limited by decoherence arising from local `environmental' interactions. Compounding this, as devices become more complex, i.e. contain multiple functional units, the `local' environments begin to overlap, creating the possibility of environmentally
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Quantum Monte Carlo simulations for financial risk analytics: scenario generation for equity, rate, and credit risk factors Quantum (IF 6.4) Pub Date : 2024-04-04 Titos Matsakos, Stuart Nield
Monte Carlo (MC) simulations are widely used in financial risk management, from estimating value-at-risk (VaR) to pricing over-the-counter derivatives. However, they come at a significant computational cost due to the number of scenarios required for convergence. If a probability distribution is available, Quantum Amplitude Estimation (QAE) algorithms can provide a quadratic speed-up in measuring its
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The qudit Pauli group: non-commuting pairs, non-commuting sets, and structure theorems Quantum (IF 6.4) Pub Date : 2024-04-04 Rahul Sarkar, Theodore J. Yoder
Qudits with local dimension $d \gt 2$ can have unique structure and uses that qubits ($d=2$) cannot. Qudit Pauli operators provide a very useful basis of the space of qudit states and operators. We study the structure of the qudit Pauli group for any, including composite, $d$ in several ways. To cover composite values of $d$, we work with modules over commutative rings, which generalize the notion
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Two-Particle Scattering on Non-Translation Invariant Line Lattices Quantum (IF 6.4) Pub Date : 2024-04-04 Luna Lima e Silva, Daniel Jost Brod
Quantum walks have been used to develop quantum algorithms since their inception, and can be seen as an alternative to the usual circuit model; combining single-particle quantum walks on sparse graphs with two-particle scattering on a line lattice is sufficient to perform universal quantum computation. In this work we solve the problem of two-particle scattering on the line lattice for a family of
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Heisenberg-limited metrology with perturbing interactions Quantum (IF 6.4) Pub Date : 2024-03-28 Chao Yin, Andrew Lucas
We show that it is possible to perform Heisenberg-limited metrology on GHZ-like states, in the presence of generic spatially local, possibly strong interactions during the measurement process. An explicit protocol, which relies on single-qubit measurements and feedback based on polynomial-time classical computation, achieves the Heisenberg limit. In one dimension, matrix product state methods can be
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Enriched string-net models and their excitations Quantum (IF 6.4) Pub Date : 2024-03-28 David Green, Peter Huston, Kyle Kawagoe, David Penneys, Anup Poudel, Sean Sanford
Boundaries of Walker-Wang models have been used to construct commuting projector models which realize chiral unitary modular tensor categories (UMTCs) as boundary excitations. Given a UMTC $\mathcal{A}$ representing the Witt class of an anomaly, the article [10] gave a commuting projector model associated to an $\mathcal{A}$-enriched unitary fusion category $\mathcal{X}$ on a 2D boundary of the 3D
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Loss-tolerant architecture for quantum computing with quantum emitters Quantum (IF 6.4) Pub Date : 2024-03-28 Matthias C. Löbl, Stefano Paesani, Anders S. Sørensen
We develop an architecture for measurement-based quantum computing using photonic quantum emitters. The architecture exploits spin-photon entanglement as resource states and standard Bell measurements of photons for fusing them into a large spin-qubit cluster state. The scheme is tailored to emitters with limited memory capabilities since it only uses an initial non-adaptive (ballistic) fusion process
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Randomized measurement protocols for lattice gauge theories Quantum (IF 6.4) Pub Date : 2024-03-27 Jacob Bringewatt, Jonathan Kunjummen, Niklas Mueller
Randomized measurement protocols, including classical shadows, entanglement tomography, and randomized benchmarking are powerful techniques to estimate observables, perform state tomography, or extract the entanglement properties of quantum states. While unraveling the intricate structure of quantum states is generally difficult and resource-intensive, quantum systems in nature are often tightly constrained
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Effective versus Floquet theory for the Kerr parametric oscillator Quantum (IF 6.4) Pub Date : 2024-03-25 Ignacio García-Mata, Rodrigo G. Cortiñas, Xu Xiao, Jorge Chávez-Carlos, Victor S. Batista, Lea F. Santos, Diego A. Wisniacki
Parametric gates and processes engineered from the perspective of the static effective Hamiltonian of a driven system are central to quantum technology. However, the perturbative expansions used to derive static effective models may not be able to efficiently capture all the relevant physics of the original system. In this work, we investigate the conditions for the validity of the usual low-order
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Efficient quantum amplitude encoding of polynomial functions Quantum (IF 6.4) Pub Date : 2024-03-21 Javier Gonzalez-Conde, Thomas W. Watts, Pablo Rodriguez-Grasa, Mikel Sanz
Loading functions into quantum computers represents an essential step in several quantum algorithms, such as quantum partial differential equation solvers. Therefore, the inefficiency of this process leads to a major bottleneck for the application of these algorithms. Here, we present and compare two efficient methods for the amplitude encoding of real polynomial functions on $n$ qubits. This case
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Sequential hypothesis testing for continuously-monitored quantum systems Quantum (IF 6.4) Pub Date : 2024-03-20 Giulio Gasbarri, Matias Bilkis, Elisabet Roda-Salichs, John Calsamiglia
We consider a quantum system that is being continuously monitored, giving rise to a measurement signal. From such a stream of data, information needs to be inferred about the underlying system's dynamics. Here we focus on hypothesis testing problems and put forward the usage of sequential strategies where the signal is analyzed in real time, allowing the experiment to be concluded as soon as the underlying
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Entanglement catalysis for quantum states and noisy channels Quantum (IF 6.4) Pub Date : 2024-03-20 Chandan Datta, Tulja Varun Kondra, Marek Miller, Alexander Streltsov
Many applications of the emerging quantum technologies, such as quantum teleportation and quantum key distribution, require singlets, maximally entangled states of two quantum bits. It is thus of utmost importance to develop optimal procedures for establishing singlets between remote parties. As has been shown very recently, singlets can be obtained from other quantum states by using a quantum catalyst
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Dissipation as a resource for Quantum Reservoir Computing Quantum (IF 6.4) Pub Date : 2024-03-20 Antonio Sannia, Rodrigo Martínez-Peña, Miguel C. Soriano, Gian Luca Giorgi, Roberta Zambrini
Dissipation induced by interactions with an external environment typically hinders the performance of quantum computation, but in some cases can be turned out as a useful resource. We show the potential enhancement induced by dissipation in the field of quantum reservoir computing introducing tunable local losses in spin network models. Our approach based on continuous dissipation is able not only
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Constant-sized self-tests for maximally entangled states and single projective measurements Quantum (IF 6.4) Pub Date : 2024-03-21 Jurij Volčič
Self-testing is a powerful certification of quantum systems relying on measured, classical statistics. This paper considers self-testing in bipartite Bell scenarios with small number of inputs and outputs, but with quantum states and measurements of arbitrarily large dimension. The contributions are twofold. Firstly, it is shown that every maximally entangled state can be self-tested with four binary
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Classical shadows based on locally-entangled measurements Quantum (IF 6.4) Pub Date : 2024-03-21 Matteo Ippoliti
We study classical shadows protocols based on randomized measurements in $n$-qubit entangled bases, generalizing the random Pauli measurement protocol ($n = 1$). We show that entangled measurements ($n\geq 2$) enable nontrivial and potentially advantageous trade-offs in the sample complexity of learning Pauli expectation values. This is sharply illustrated by shadows based on two-qubit Bell measurements:
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Beyond-adiabatic Quantum Admittance of a Semiconductor Quantum Dot at High Frequencies: Rethinking Reflectometry as Polaron Dynamics Quantum (IF 6.4) Pub Date : 2024-03-21 L. Peri, G. A. Oakes, L. Cochrane, C. J. B. Ford, M. F. Gonzalez-Zalba
Semiconductor quantum dots operated dynamically are the basis of many quantum technologies such as quantum sensors and computers. Hence, modelling their electrical properties at microwave frequencies becomes essential to simulate their performance in larger electronic circuits. Here, we develop a self-consistent quantum master equation formalism to obtain the admittance of a quantum dot tunnel-coupled
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Transformations in quantum networks via local operations assisted by finitely many rounds of classical communication Quantum (IF 6.4) Pub Date : 2024-03-14 Cornelia Spee, Tristan Kraft
Recent advances have led towards first prototypes of quantum networks in which entanglement is distributed by sources producing bipartite entangled states. This raises the question of which states can be generated in quantum networks based on bipartite sources using local operations and classical communication. In this work, we study state transformations under finite rounds of local operations and
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Can Error Mitigation Improve Trainability of Noisy Variational Quantum Algorithms? Quantum (IF 6.4) Pub Date : 2024-03-14 Samson Wang, Piotr Czarnik, Andrew Arrasmith, M. Cerezo, Lukasz Cincio, Patrick J. Coles
Variational Quantum Algorithms (VQAs) are often viewed as the best hope for near-term quantum advantage. However, recent studies have shown that noise can severely limit the trainability of VQAs, e.g., by exponentially flattening the cost landscape and suppressing the magnitudes of cost gradients. Error Mitigation (EM) shows promise in reducing the impact of noise on near-term devices. Thus, it is
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Teleportation of Post-Selected Quantum States Quantum (IF 6.4) Pub Date : 2024-03-14 Daniel Collins
Teleportation allows Alice to send a pre-prepared quantum state to Bob using only pre-shared entanglement and classical communication. Here we show that it is possible to teleport a state which is also $\it{post}$-selected. Post-selection of a state $\Phi$ means that after Alice has finished her experiment she performs a measurement and only keeps runs of the experiment where the measurement outcome
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Compiling Quantum Circuits for Dynamically Field-Programmable Neutral Atoms Array Processors Quantum (IF 6.4) Pub Date : 2024-03-14 Daniel Bochen Tan, Dolev Bluvstein, Mikhail D. Lukin, Jason Cong
Dynamically field-programmable qubit arrays (DPQA) have recently emerged as a promising platform for quantum information processing. In DPQA, atomic qubits are selectively loaded into arrays of optical traps that can be reconfigured during the computation itself. Leveraging qubit transport and parallel, entangling quantum operations, different pairs of qubits, even those initially far away, can be
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Entanglement Trajectory and its Boundary Quantum (IF 6.4) Pub Date : 2024-03-14 Ruge Lin
In this article, we present a novel approach to investigating entanglement in the context of quantum computing. Our methodology involves analyzing reduced density matrices at different stages of a quantum algorithm's execution and representing the dominant eigenvalue and von Neumann entropy on a graph, creating an "entanglement trajectory." To establish the trajectory's boundaries, we employ random
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A structure theorem for generalized-noncontextual ontological models Quantum (IF 6.4) Pub Date : 2024-03-14 David Schmid, John H. Selby, Matthew F. Pusey, Robert W. Spekkens
It is useful to have a criterion for when the predictions of an operational theory should be considered classically explainable. Here we take the criterion to be that the theory admits of a generalized-noncontextual ontological model. Existing works on generalized noncontextuality have focused on experimental scenarios having a simple structure: typically, prepare-measure scenarios. Here, we formally
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Basic quantum subroutines: finding multiple marked elements and summing numbers Quantum (IF 6.4) Pub Date : 2024-03-14 Joran van Apeldoorn, Sander Gribling, Harold Nieuwboer
We show how to find all $k$ marked elements in a list of size $N$ using the optimal number $O(\sqrt{N k})$ of quantum queries and only a polylogarithmic overhead in the gate complexity, in the setting where one has a small quantum memory. Previous algorithms either incurred a factor $k$ overhead in the gate complexity, or had an extra factor $\log(k)$ in the query complexity. We then consider the problem
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Stabilization of Hubbard-Thouless pumps through nonlocal fermionic repulsion Quantum (IF 6.4) Pub Date : 2024-03-14 Javier Argüello-Luengo, Manfred J. Mark, Francesca Ferlaino, Maciej Lewenstein, Luca Barbiero, Sergi Julià-Farré
Thouless pumping represents a powerful concept to probe quantized topological invariants in quantum systems. We explore this mechanism in a generalized Rice-Mele Fermi-Hubbard model characterized by the presence of competing onsite and intersite interactions. Contrary to recent experimental and theoretical results, showing a breakdown of quantized pumping induced by the onsite repulsion, we prove that
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Quantum circuits for toric code and X-cube fracton model Quantum (IF 6.4) Pub Date : 2024-03-13 Penghua Chen, Bowen Yan, Shawn X. Cui
We propose a systematic and efficient quantum circuit composed solely of Clifford gates for simulating the ground state of the surface code model. This approach yields the ground state of the toric code in $\lceil 2L+2+log_{2}(d)+\frac{L}{2d} \rceil$ time steps, where $L$ refers to the system size and $d$ represents the maximum distance to constrain the application of the CNOT gates. Our algorithm
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Variational Phase Estimation with Variational Fast Forwarding Quantum (IF 6.4) Pub Date : 2024-03-13 Maria-Andreea Filip, David Muñoz Ramo, Nathan Fitzpatrick
Subspace diagonalisation methods have appeared recently as promising means to access the ground state and some excited states of molecular Hamiltonians by classically diagonalising small matrices, whose elements can be efficiently obtained by a quantum computer. The recently proposed Variational Quantum Phase Estimation (VQPE) algorithm uses a basis of real time-evolved states, for which the energy
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Time-optimal multi-qubit gates: Complexity, efficient heuristic and gate-time bounds Quantum (IF 6.4) Pub Date : 2024-03-13 Pascal Baßler, Markus Heinrich, Martin Kliesch
Multi-qubit entangling interactions arise naturally in several quantum computing platforms and promise advantages over traditional two-qubit gates. In particular, a fixed multi-qubit Ising-type interaction together with single-qubit X-gates can be used to synthesize global ZZ-gates (GZZ gates). In this work, we first show that the synthesis of such quantum gates that are time-optimal is NP-hard. Second
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Here comes the SU(N): multivariate quantum gates and gradients Quantum (IF 6.4) Pub Date : 2024-03-07 Roeland Wiersema, Dylan Lewis, David Wierichs, Juan Carrasquilla, Nathan Killoran
Variational quantum algorithms use non-convex optimization methods to find the optimal parameters for a parametrized quantum circuit in order to solve a computational problem. The choice of the circuit ansatz, which consists of parameterized gates, is crucial to the success of these algorithms. Here, we propose a gate which fully parameterizes the special unitary group $\mathrm{SU}(N)$. This gate is
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Ergodicity Breaking Under Confinement in Cold-Atom Quantum Simulators Quantum (IF 6.4) Pub Date : 2024-02-29 Jean-Yves Desaules, Guo-Xian Su, Ian P. McCulloch, Bing Yang, Zlatko Papić, Jad C. Halimeh
The quantum simulation of gauge theories on synthetic quantum matter devices has gained a lot of traction in the last decade, making possible the observation of a range of exotic quantum many-body phenomena. In this work, we consider the spin-$1/2$ quantum link formulation of $1+1$D quantum electrodynamics with a topological $\theta$-angle, which can be used to tune a confinement-deconfinement transition
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Bicolor loop models and their long range entanglement Quantum (IF 6.4) Pub Date : 2024-02-29 Zhao Zhang
Quantum loop models are well studied objects in the context of lattice gauge theories and topological quantum computing. They usually carry long range entanglement that is captured by the topological entanglement entropy. I consider generalization of the toric code model to bicolor loop models and show that the long range entanglement can be reflected in three different ways: a topologically invariant
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Identifying families of multipartite states with non-trivial local entanglement transformations Quantum (IF 6.4) Pub Date : 2024-02-29 Nicky Kai Hong Li, Cornelia Spee, Martin Hebenstreit, Julio I. de Vicente, Barbara Kraus
The study of state transformations by spatially separated parties with local operations assisted by classical communication (LOCC) plays a crucial role in entanglement theory and its applications in quantum information processing. Transformations of this type among pure bipartite states were characterized long ago and have a revealing theoretical structure. However, it turns out that generic fully
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Dynamical quantum phase transitions from random matrix theory Quantum (IF 6.4) Pub Date : 2024-02-29 David Pérez-García, Leonardo Santilli, Miguel Tierz
We uncover a novel dynamical quantum phase transition, using random matrix theory and its associated notion of planar limit. We study it for the isotropic XY Heisenberg spin chain. For this, we probe its real-time dynamics through the Loschmidt echo. This leads to the study of a random matrix ensemble with a complex weight, whose analysis requires novel technical considerations, that we develop. We
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Entanglement-symmetries of covariant channels Quantum (IF 6.4) Pub Date : 2024-02-29 Dominic Verdon
Let $G$ and $G'$ be monoidally equivalent compact quantum groups, and let $H$ be a Hopf-Galois object realising a monoidal equivalence between these groups' representation categories. This monoidal equivalence induces an equivalence Chan($G$) $\rightarrow$ Chan($G'$), where Chan($G$) is the category whose objects are finite-dimensional $C*$-algebras with an action of G and whose morphisms are covariant
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Entanglement dynamics of photon pairs and quantum memories in the gravitational field of the earth Quantum (IF 6.4) Pub Date : 2024-02-29 Roy Barzel, Mustafa Gündoğan, Markus Krutzik, Dennis Rätzel, Claus Lämmerzahl
We investigate the effect of entanglement dynamics due to gravity – the basis of a mechanism of universal decoherence – for photonic states and quantum memories in Mach-Zehnder and Hong-Ou-Mandel interferometry setups in the gravitational field of the earth. We show that chances are good to witness the effect with near-future technology in Hong-Ou-Mandel interferometry. This would represent an experimental
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Towards a measurement theory in QFT: “Impossible” quantum measurements are possible but not ideal Quantum (IF 6.4) Pub Date : 2024-02-27 Nicolas Gisin, Flavio Del Santo
Naive attempts to put together relativity and quantum measurements lead to signaling between space-like separated regions. In QFT, these are known as $\textit{impossible measurements}$. We show that the same problem arises in non-relativistic quantum physics, where joint nonlocal measurements (i.e., between systems kept spatially separated) in general lead to signaling, while one would expect no-signaling
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Improved Accuracy for Trotter Simulations Using Chebyshev Interpolation Quantum (IF 6.4) Pub Date : 2024-02-26 Gumaro Rendon, Jacob Watkins, Nathan Wiebe
Quantum metrology allows for measuring properties of a quantum system at the optimal Heisenberg limit. However, when the relevant quantum states are prepared using digital Hamiltonian simulation, the accrued algorithmic errors will cause deviations from this fundamental limit. In this work, we show how algorithmic errors due to Trotterized time evolution can be mitigated through the use of standard
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Analogue Quantum Simulation with Fixed-Frequency Transmon Qubits Quantum (IF 6.4) Pub Date : 2024-02-22 Sean Greenaway, Adam Smith, Florian Mintert, Daniel Malz
We experimentally assess the suitability of transmon qubits with fixed frequencies and fixed interactions for the realization of analogue quantum simulations of spin systems. We test a set of necessary criteria for this goal on a commercial quantum processor using full quantum process tomography and more efficient Hamiltonian tomography. Significant single qubit errors at low amplitudes are identified
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Accelerating Quantum Algorithms with Precomputation Quantum (IF 6.4) Pub Date : 2024-02-22 William J. Huggins, Jarrod R. McClean
Real-world applications of computing can be extremely time-sensitive. It would be valuable if we could accelerate such tasks by performing some of the work ahead of time. Motivated by this, we propose a cost model for quantum algorithms that allows quantum precomputation; i.e., for a polynomial amount of ``free'' computation before the input to an algorithm is fully specified, and methods for taking
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Quantum Vision Transformers Quantum (IF 6.4) Pub Date : 2024-02-22 El Amine Cherrat, Iordanis Kerenidis, Natansh Mathur, Jonas Landman, Martin Strahm, Yun Yvonna Li
In this work, quantum transformers are designed and analysed in detail by extending the state-of-the-art classical transformer neural network architectures known to be very performant in natural language processing and image analysis. Building upon the previous work, which uses parametrised quantum circuits for data loading and orthogonal neural layers, we introduce three types of quantum transformers
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Stabilizer Formalism for Operator Algebra Quantum Error Correction Quantum (IF 6.4) Pub Date : 2024-02-21 Guillaume Dauphinais, David W. Kribs, Michael Vasmer
We introduce a stabilizer formalism for the general quantum error correction framework called operator algebra quantum error correction (OAQEC), which generalizes Gottesman's formulation for traditional quantum error correcting codes (QEC) and Poulin's for operator quantum error correction and subsystem codes (OQEC). The construction generates hybrid classical-quantum stabilizer codes and we formulate
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Taming the Rotating Wave Approximation Quantum (IF 6.4) Pub Date : 2024-02-21 Daniel Burgarth, Paolo Facchi, Robin Hillier, Marilena Ligabò
The interaction between light and matter is one of the oldest research areas of quantum mechanics, and a field that just keeps on delivering new insights and applications. With the arrival of cavity and circuit quantum electrodynamics we can now achieve strong light-matter couplings which form the basis of most implementations of quantum technology. But quantum information processing also has high
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A hybrid quantum algorithm to detect conical intersections Quantum (IF 6.4) Pub Date : 2024-02-20 Emiel Koridon, Joana Fraxanet, Alexandre Dauphin, Lucas Visscher, Thomas E. O'Brien, Stefano Polla
Conical intersections are topologically protected crossings between the potential energy surfaces of a molecular Hamiltonian, known to play an important role in chemical processes such as photoisomerization and non-radiative relaxation. They are characterized by a non-zero Berry phase, which is a topological invariant defined on a closed path in atomic coordinate space, taking the value $\pi$ when
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Reqomp: Space-constrained Uncomputation for Quantum Circuits Quantum (IF 6.4) Pub Date : 2024-02-19 Anouk Paradis, Benjamin Bichsel, Martin Vechev
Quantum circuits must run on quantum computers with tight limits on qubit and gate counts. To generate circuits respecting both limits, a promising opportunity is exploiting $uncomputation$ to trade qubits for gates. We present Reqomp, a method to automatically synthesize correct and efficient uncomputation of ancillae while respecting hardware constraints. For a given circuit, Reqomp can offer a wide
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Photonic entanglement during a zero-g flight Quantum (IF 6.4) Pub Date : 2024-02-15 Julius Arthur Bittermann, Lukas Bulla, Sebastian Ecker, Sebastian Philipp Neumann, Matthias Fink, Martin Bohmann, Nicolai Friis, Marcus Huber, Rupert Ursin
Quantum technologies have matured to the point that we can test fundamental quantum phenomena under extreme conditions. Specifically, entanglement, a cornerstone of modern quantum information theory, can be robustly produced and verified in various adverse environments. We take these tests further and implement a high-quality Bell experiment during a parabolic flight, transitioning from microgravity
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Quantitative relations between different measurement contexts Quantum (IF 6.4) Pub Date : 2024-02-14 Ming Ji, Holger F. Hofmann
In quantum theory, a measurement context is defined by an orthogonal basis in a Hilbert space, where each basis vector represents a specific measurement outcome. The precise quantitative relation between two different measurement contexts can thus be characterized by the inner products of nonorthogonal states in that Hilbert space. Here, we use measurement outcomes that are shared by different contexts
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Continuous-time quantum walks for MAX-CUT are hot Quantum (IF 6.4) Pub Date : 2024-02-13 Robert J. Banks, Ehsan Haque, Farah Nazef, Fatima Fethallah, Fatima Ruqaya, Hamza Ahsan, Het Vora, Hibah Tahir, Ibrahim Ahmad, Isaac Hewins, Ishaq Shah, Krish Baranwal, Mannan Arora, Mateen Asad, Mubasshirah Khan, Nabian Hasan, Nuh Azad, Salgai Fedaiee, Shakeel Majeed, Shayam Bhuyan, Tasfia Tarannum, Yahya Ali, Dan E. Browne, P. A. Warburton
By exploiting the link between time-independent Hamiltonians and thermalisation, heuristic predictions on the performance of continuous-time quantum walks for MAX-CUT are made. The resulting predictions depend on the number of triangles in the underlying MAX-CUT graph. We extend these results to the time-dependent setting with multi-stage quantum walks and Floquet systems. The approach followed here
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Incompatibility of quantum instruments Quantum (IF 6.4) Pub Date : 2024-02-12 Leevi Leppäjärvi, Michal Sedlák
Quantum instruments describe outcome probability as well as state change induced by measurement of a quantum system. Incompatibility of two instruments, i. e. the impossibility to realize them simultaneously on a given quantum system, generalizes incompatibility of channels and incompatibility of positive operator-valued measures (POVMs). We derive implications of instrument compatibility for the induced
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Gravitational quantum switch on a superposition of spherical shells Quantum (IF 6.4) Pub Date : 2024-02-12 Natália S. Móller, Bruna Sahdo, Nelson Yokomizo
In the absence of a complete theory of quantum gravity, phenomenological models built upon minimal assumptions have been explored for the analysis of possible quantum effects in gravitational systems. Implications of a superposition of geometries have been considered in such models, including the occurrence of processes with indefinite order. In a gravitational quantum switch, in particular, the order
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Stabilizer Codes with Exotic Local-dimensions Quantum (IF 6.4) Pub Date : 2024-02-12 Lane G. Gunderman
Traditional stabilizer codes operate over prime power local-dimensions. In this work we extend the stabilizer formalism using the local-dimension-invariant setting to import stabilizer codes from these standard local-dimensions to other cases. In particular, we show that any traditional stabilizer code can be used for analog continuous-variable codes, and consider restrictions in phase space and discretized
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Efficient learning of $t$-doped stabilizer states with single-copy measurements Quantum (IF 6.4) Pub Date : 2024-02-12 Nai-Hui Chia, Ching-Yi Lai, Han-Hsuan Lin
One of the primary objectives in the field of quantum state learning is to develop algorithms that are time-efficient for learning states generated from quantum circuits. Earlier investigations have demonstrated time-efficient algorithms for states generated from Clifford circuits with at most $\log(n)$ non-Clifford gates. However, these algorithms necessitate multi-copy measurements, posing implementation
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Impact of conditional modelling for a universal autoregressive quantum state Quantum (IF 6.4) Pub Date : 2024-02-08 Massimo Bortone, Yannic Rath, George H. Booth
We present a generalized framework to adapt universal quantum state approximators, enabling them to satisfy rigorous normalization and autoregressive properties. We also introduce filters as analogues to convolutional layers in neural networks to incorporate translationally symmetrized correlations in arbitrary quantum states. By applying this framework to the Gaussian process state, we enforce autoregressive
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Efficient classical simulation of cluster state quantum circuits with alternative inputs Quantum (IF 6.4) Pub Date : 2024-02-06 Sahar Atallah, Michael Garn, Sania Jevtic, Yukuan Tao, Shashank Virmani
We provide new examples of pure entangled systems related to cluster state quantum computation that can be efficiently simulated classically. In cluster state quantum computation input qubits are initialised in the `equator' of the Bloch sphere, $CZ$ gates are applied, and finally the qubits are measured adaptively using $Z$ measurements or measurements of $\cos(\theta)X + \sin(\theta)Y$ operators