Quantum Physics
Yu Wu, Qianli Zhou, Jie Geng et al. (+2 more)
Multimodal learning aims to enhance perceptual and decision-making capabilities by integrating information from diverse sources. However, classical deep learning approaches face a critical trade-off between the high accuracy of black-box feature-level fusion and the interpretability of less outstanding decision-level fusion, alongside the challenges of parameter explosion and complexity. This paper discusses the accuracy-interpretablity-complexity dilemma under the
quantum computation framework and propose a feature
entanglement-based
quantum multimodal fusion neural network. The model is composed of three core components: a classical feed-forward module for unimodal processing, an interpretable
quantum fusion block, and a
quantum convolutional neural network (QCNN) for deep feature extraction. By leveraging the strong expressive power of
quantum, we have reduced the complexity of
multimodal fusion and post-processing to linear, and the fusion process also possesses the interpretability of decision-level fusion. The simulation results demonstrate that our model achieves classification accuracy comparable to classical networks with dozens of times of parameters, exhibiting notable stability and performance across
multimodal image
datasets.
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All authors Yu Wu, Qianli Zhou, Jie Geng, Xinyang Deng, Wen Jiang
Quantum Physics
LOTUS: Layer-ordered Temporally Unified Schedules For Quantum Approximate Optimization Algorithms
Phuong-Nam Nguyen
In this paper, we introduce LOTUS (Layer-Ordered Temporally-Unified Schedules), which is a framework that restructures QAOA from a high-dimensional, chaotic search into a low-dimensional dynamical system. By replacing independent layer-wise angles with a Hybrid
Fourier-Autoregressive (HFA) mapping, LOTUS enforces global temporal coherence while maintaining local flexibility. LOTUS consistently outperforms standard optimizers, achieving up to a $27.2\%$ improvement in expectation values over L-BFGS-B and $20.8\%$ compared with COBYLA. Besides, our proposed method drastically reduces computational costs, requiring over $90\%$ fewer iterations than methods like Powell or SLSQP.
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Quantum Physics · Cross-listed from physics.atom-ph
Controlling Rydberg atom-polariton interactions: from exceptional points to fast readout
Tamara Šumarac, Emily H. Qiu, Shai Tsesses et al. (+8 more)
Rydberg atoms represent a platform underpinning many recent developments in
quantum computation, simulation, sensing, and metrology. They further facilitate optical nonlinearity at the single-
photon level when coupled to
photons propagating in atomic clouds, which form collective atomic excitations called Rydberg polaritons, strongly interacting with each other. Here, we experimentally explore interactions between a Rydberg polariton in an atomic ensemble and a single, adjacent, Rydberg atom. We discover three different regimes of
quantum dynamics corresponding to polariton blockade, coherent exchange, and probabilistic hopping, which are defined by their distinct transmission characteristics, with a transition through an exceptional point occurring between blockade and coherent exchange. We investigate the applications of such interactions for fast, non-destructive detection of Rydberg atoms and present proof-of-principle demonstrations for their potential application in nonlinear photonic networks.
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All authors Tamara Šumarac, Emily H. Qiu, Shai Tsesses, Peiran Niu, Adrian J. Menssen, Wenchao Xu, Valentin Walther, Uroš Delić, Soonwon Choi, Mikhail D. Lukin, Vladan Vuletić
Quantum Physics
Bipartitioning of Graph States for Distributed Measurement-Based Quantum Computing
Kjell Fredrik Pettersen, Matthias Heller, Giorgio Sartor et al. (+1 more)
Measurement-Based
Quantum Computing (MBQC) is inherently well-suited for Distributed
Quantum Computing (DQC): once a resource state is prepared and distributed across a network of
quantum nodes, computation proceeds through local measurements coordinated by classical communication. However, since non-local gates acting on different
Quantum Processing Units (QPUs) are a bottleneck, it is crucial to optimize the
qubit assignment to minimize inter-node
entanglement of the shared resource. For graph state resources shared across two QPUs, this task reduces to finding bipartitions with minimal cut rank. We introduce a simulated annealing-based
algorithm that efficiently updates the cut rank when two vertices swap sides across a bipartition, such that computing the new cut rank from scratch, which would be much more expensive, is not necessary. We show that the approach is highly effective for determining
qubit assignments in distributed MBQC by testing it on grid graphs and the measurement-based
Quantum Approximate Optimization
Algorithm (QAOA).
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All authors Kjell Fredrik Pettersen, Matthias Heller, Giorgio Sartor, Raoul Heese
Quantum Physics · Cross-listed from physics.atom-ph
Creation and precise spectroscopy of $^{86}$Sr$_2$ halo molecules
Brandon Iritani, Jingjing Huang, Wenwei Xu et al. (+3 more)
We report on the creation of $^{86}$Sr$_2$ molecules in the
halo state and neighboring weakly bound states. Efficient molecule production via one-
photon photoassociation relies on sufficient wavefunction overlap between the target vibrational states in the electronic excited- and ground-state potentials. Using Autler-Townes spectroscopy, transition strengths are measured to identify optimal pathways for production of weakly bound molecules. Vibrational splittings for the three least-bound vibrational states are measured, and dominant systematic uncertainties are evaluated with uncertainties below 100 Hz. From these splittings, absolute binding energies for these weakly bound vibrational states are determined. The results pave the way to a molecular isotope shift measurement with Sr$_2$.
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All authors Brandon Iritani, Jingjing Huang, Wenwei Xu, Gisung Sim, Robert Moszynski, Tanya Zelevinsky
Quantum Physics
Looking for Work in Quantum Thermodynamics
Eugene Y. S. Chua
This paper diagnoses a much-discussed problem in
quantum thermodynamics, that of generalizing classical work into the
quantum domain. I begin with the no-go
theorem of Perarnau-Llobet et al (2017): no universal measurement scheme for
quantum work satisfies two intuitive, classically consilient desiderata. I assess this incompatibility as stemming from the measurement problem. Decoherence restores compatibility for all practical purposes, but raises questions about what 'universality' should mean and whether any measurement scheme can be 'universal'. I consider a different standard of universality – in terms of ontology – by defining a trajectory-based notion of
quantum work using the
quantum potential. While this preserves the classical role of work as the integral of forces over distances, and evades the tension of the no-go
theorem, consilience fails elsewhere; no single
quantum work concept seems capable of preserving all classical features, raising questions for what it takes for successful generalization of the work concept to
quantum thermodynamics.
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Quantum Physics
The pros and cons of using deep reinforcement learning or genetic algorithms to design control schemes for quantum state transfer on qubit chains
Sofía Perón Santana, Ariel Fiuri, Martín Domínguez et al. (+1 more)
In recent years, control methods based on different optimization techniques have shed light on the possibilities of processing information in many
quantum systems. When exploring the transmission of
quantum states, faster transmission times are mandatory to avoid the deleterious effects of multiple sources of decoherence that spoil the transmission process. In particular, using Reinforcement Learning to devise sequences of step-wise external controls provides good transfer policies at short transmission times. We present two approaches to control the transmission of
quantum states in
qubit chains using external controls to force the dynamical
evolution of the chain state. The first approach relies on the well-known Genetic
Algorithm to generate a sequence of external controls, while the second approach uses a variant of Reinforcement Learning. The Genetic
algorithm achieves excellent transmission fidelity at as short transmission times as Reinforcement Learning, surpassing the fidelities achieved by the latter method. Nevertheless, the Reinforcement Learning method offers robust control policies when the control pulses are noisy enough, owing to an imperfect timing of the pulses, deficient control devices, or other sources of phase decoherence. We present the regime where each method is best suited to control the transmission of arbitrary
qubit states.
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All authors Sofía Perón Santana, Ariel Fiuri, Martín Domínguez, Omar Osenda
Quantum Physics
Quantum algorithm for dephasing of coupled systems: decoupling and IQP duality
Sabrina Yue Wang and Raul A. Santos
Noise and decoherence are ubiquitous in the dynamics of
quantum systems coupled to an external environment. In the regime where environmental correlations decay rapidly, the
evolution of a subsytem is well described by a Lindblad
quantum master equation. In this work, we introduce a
quantum algorithm for simulating unital Lindbladian dynamics by sampling
unitary quantum channels without extra ancillas. Using ancillary
qubits we show that this
algorithm allows approximating general Lindbladians as well. For interacting dephasing Lindbladians coupling two subsystems, we develop a decoupling scheme that reduces the
circuit complexity of the simulation. This is achieved by sampling from a time-correlated probability distribution - determined by the
evolution of one subsystem, which specifies the
stochastic circuit implemented on the complementary subsystem. We demonstrate our approach by studying a model of
bosons coupled to
fermions via dephasing, which naturally arises from anharmonic effects in an electron-
phonon system coupled to a bath. Our method enables tracing out the bosonic degrees of freedom, reducing part of the dynamics to sampling an IQP
circuit. The sampled bitstrings then define a corresponding fermionic problem, which in the non-interacting case can be solved efficiently classically. We comment on the computational complexity of this class of dissipative problems, using the known fact that sampling from IQP
circuits is believed to be difficult classically.
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Quantum Physics · Cross-listed from cs.SE
Mining Quantum Software Patterns in Open-Source Projects
Neilson Carlos Leite Ramalho, Erico A. da Silva, Higor Amario de Souza et al. (+1 more)
Quantum computing has become an active research field in recent years, as its applications in fields such as cryptography, optimization, and materials science are promising. Along with these developments, challenges and opportunities exist in the field of
Quantum Software Engineering, as the development of frameworks and higher-level abstractions has attracted practitioners from diverse backgrounds. Unlike initial
quantum frameworks based on the
circuit model, recent frameworks and libraries leverage higher-level abstractions for creating
quantum programs. This paper presents an empirical study of 985 Jupyter Notebooks from 80 open-source projects to investigate how
quantum patterns are applied in practice. Our work involved two main stages. First, we built a knowledge base from three
quantum computing frameworks (Qiskit, PennyLane, and Classiq). This process led us to identify and document 9 new patterns that refine and extend the existing
quantum computing pattern catalog. Second, we developed a reusable semantic search tool to automatically detect these patterns across our large-scale
dataset, providing a practitioner-focused analysis. Our results show that developers use patterns in three levels: from foundational
circuit utilities, to common algorithmic primitives (e.g., Amplitude Amplification), up to domain-specific applications for finance and optimization. This indicates a maturing field where developers are increasingly using high-level building blocks to solve real-world problems.
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All authors Neilson Carlos Leite Ramalho, Erico A. da Silva, Higor Amario de Souza, Marcos Lordello Chaim
Quantum Physics
Latent splitting as a causal probe
Santiago Zamora, Pedro Lauand, Isadora Veeren et al. (+2 more)
Generalizations of Bell's framework to causal networks have yielded new foundational insights and applications, including the use of interventions to enhance the detection of nonclassicality in scenarios with communication. Such interventions, however, become uninformative when all observable variables are space-like separated. To address this limitation, we introduce the latent splitting procedure, a generalization of interventions to
quantum networks in which controlled manipulations are applied to latent
quantum systems. We show that latent splitting enables the detection of nonclassicality by combining observational and interventional data even when conventional interventions fail. Focusing on the triangle network, we derive new analytical witnesses that robustly certify nonclassicality, including nonlinear inequalities for minimal binary-variable scenarios and extensions of the nonclassical region of previously proposed experiments.
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All authors Santiago Zamora, Pedro Lauand, Isadora Veeren, Davide Poderini, Rafael Chaves
Quantum Physics
Universal Predictors for Mixing Time more than Liouvillian Gap
Yi-Neng Zhou
We analyze the mixing time of open
quantum systems governed by the Lindblad master equation, showing that it is determined not only by the Liouvillian gap, but also by the trace-norm factor of each decaying Liouvillian eigenmode. By utilizing them as universal predictors of mixing time, we establish general conditions for the fast and rapid mixing, respectively. Specifically, we derive rapid mixing conditions for both the strong and weak dissipation regimes, formulated as sparsity constraints on the
Hamiltonian and the local Lindblad operators. Our findings provide a general framework for calculating mixing time and offer a guide for designing dissipation to achieve desired mixing speeds, which has significant implications for efficient experimental state preparation.
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Quantum Physics
The Qutrit Bloch Sphere
Vinod K Mishra
It is very important to understand if a qutrit can be visualized in a 3-dimensional Bloch sphere. In this work, a mathematical model for performing this operation is presented.
Quantum Physics · Cross-listed from cond-mat.stat-mech
Slow mixing and emergent one-form symmetries in three-dimensional $\mathbb{Z}_2$ gauge theory
Charles Stahl, Benedikt Placke, Vedika Khemani et al. (+1 more)
Symmetry-breaking order at low temperatures is often accompanied by slow relaxation dynamics, due to diverging free-energy barriers arising from interfaces between different ordered states. Here, we extend this correspondence to classical topological order, where the ordered states are locally indistinguishable, so there is no notion of interfaces between them. We study the relaxation dynamics of the three-dimensional (3D) classical $\mathbb{Z}_2$
lattice gauge theory (LGT) as a canonical example. We prove a lower bound on the mixing time in the deconfined phase, $t_{\text{mix}} = \exp [\Omega(L)]$, where L is the linear system size. This bound applies even in the presence of perturbations that explicitly break the one-form
symmetry between different long-lived states. This perturbation destroys the energy barriers between ordered states, but we show that entropic effects nevertheless lead to diverging free-energy barriers at nonzero temperature. Our proof establishes the LGT as a robust finite-temperature classical
memory. We further prove that entropic effects lead to an emergent one-form
symmetry, via a notion that we make precise. We argue that the exponential mixing time follows from universal properties of the deconfined phase, and numerically corroborate this expectation by exploring mixing time scales at the
Higgs and confinement transitions out of the deconfined phase. These transitions are found to exhibit markedly different dynamic scaling, even though both have the static critical exponents of the 3D Ising model. We expect this novel entropic mechanism for
memory and emergent
symmetry to also bring insight into self-correcting
quantum memories.
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All authors Charles Stahl, Benedikt Placke, Vedika Khemani, Yaodong Li
Quantum Physics · Cross-listed from physics.optics
Scaleable LED-pumped Room-temperature Maser using a Multi-blade Optical Injector
Mingyang Liu, Zike Cheng, Ziqiu Huang et al. (+3 more)
Though the performance of room-temperature masers has improved over the last decade, relatively little
attention has been paid to the optics used to pump the maser's gain medium. In this work, we investigate a novel multi-blade optical “injector” that permits more effective and more scaleable pumping. The reported work encompasses an interdisciplinary mix of conceptualization, simulation,
crystal growth, fabrication, and microwave engineering. Our gain medium is pentacene dissolved as a solid solution with para-terphenyl (Pc:PTP) molecular
crystal. We accurately determine this pentacene's molecular absorption cross-section as a function of wavelength. Ray-tracing is then used to assess how different designs of waveguide inject light into the Pc:PTP
crystal. A multi-blade injector made of high-refractive-index glass (namely Ohara S-TIH6) is predicted to pump it more completely and uniformly than previous designs. Upon hand-fabricating such an injector and Bridgman-growing a
crystal of 0.1% Pc:PTP over it, an experimental maser oscillator using this combined injector-
crystal assembly is demonstrated. The performance and scaleability of multiblade injection vis-a-vis alternative strategies is analyzed.
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All authors Mingyang Liu, Zike Cheng, Ziqiu Huang, Yifan Yu, Michael Newns, Mark Oxborrow
Quantum Physics · Cross-listed from math.OA
Generalized Poincaré inequality for quantum Markov semigroups
Marius Junge and Jia Wang
We prove a noncommutative $p$-Poincaré inequality for GNS-detailed-balance
quantum Markov
semigroups (QMSs) on non-tracial $\sigma$-finite von Neumann
algebras, assuming only the existence of a spectral gap. Extending the semi-commutative results of Huang and Tropp, we first establish the inequality for tracial von Neumann
algebras. We use Markov dilations to obtain chain-rule estimates for Dirichlet forms and amalgamated free products to define an appropriate noncommutative derivation. We then extend the result to QMSs satisfying GNS detailed balance on non-tracial $\sigma$-finite von Neumann
algebras, using Haagerup's reduction and Kosaki's interpolation
theorem. As applications, we recover sub-exponential concentration inequalities and estimate the Lipschitz and completely bounded Lipschitz diameters of the QMSs.
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Quantum Physics
From Superradiance to Superabsorption: An Exact Treatment of Non-Markovian Cooperative Radiation
Ignacio González and Ángel Rivas
We investigate the emergence of cooperative radiation phenomena in ensembles of two-level atoms coupled to a lossy resonant cavity beyond the Markovian and mean-field approximations. By deriving a complete analytical solution for the two-emitter case and employing a numerically exact method for larger ensembles, we characterize the full transition from Markovian to non-Markovian collective dynamics for systems of up to $10^3$ emitters. Our results reveal three distinct regimes: a Markovian phase exhibiting the standard superradiant burst, a non-Markovian phase featuring spontaneous superabsorption of the emitted field, and a critical regime marked by pulsed collective emission. We show that the critical spectral width separating these behaviors increases monotonically with the number of emitters, demonstrating that environmental
memory effects can be enhanced by cooperativity. Finally, we find that the superradiant scaling of the peak intensity progressively degrades with increasing system size, approaching a subquadratic law in the limit of a perfect cavity. In this regime, spontaneous superabsorption emerges as a distinct manifestation of non-Markovian cooperativity.
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Quantum Physics
Counterdiabatic ADAPT-VQE for molecular simulation
Diego Tancara, Herbert Díaz-Moraga and Dardo Goyeneche
Among variational
quantum algorithms designed for NISQ devices, ADAPT-VQE stands out for its robustness against barren plateaus, particularly in estimating molecular ground states. On the other hand, counterdiabatic
algorithms have shown advantages in both performance and
circuit depth when compared to standard adiabatic approaches. In this work, we propose a hybrid method that integrates the ADAPT-VQE framework with counterdiabatic driving within an adiabatic
evolution scheme. Specifically, we map the molecular
Hamiltonian to a
qubit representation and construct an adiabatic
Hamiltonian, from which an approximate adiabatic gauge potential is computed using nested commutators. The resulting operator terms define the operator pool, and the ADAPT-VQE
algorithm is applied to iteratively select the most relevant elements for the ansatz. Our results demonstrate improvements in performance and reductions in
circuit depth compared to using either counterdiabatic
algorithms or ADAPT-VQE with fermionic excitation operators, thus supporting the effectiveness of combining both paradigms in molecular simulations.
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Quantum Physics
Continuous-time noise mitigation in analogue quantum simulation
Gabriele Bressanini, Yue Ma, Hyukjoon Kwon et al. (+1 more)
Analogue
quantum simulators offer a promising route to explore
quantum many-body dynamics beyond classical reach in the near term. However, their vulnerability to noise limits the accuracy of simulations. Here, we establish a new framework for mitigating noise in analogue
quantum simulation, operating in a time-continuous manner. To our knowledge, this is the first protocol that is fully analogue and that achieves exact noise cancellation. Our method requires a small number of ancillary
qubits, whose interaction with the system$-$combined with classical post-processing of joint measurement data$-$is tailored to cancel the effect of noise. Furthermore, the protocol is
Hamiltonian-independent, robust to realistic ancilla noise, and avoids any discretization, preserving the continuous-time nature of the system's dynamics. This work opens a new direction for achieving high-fidelity analogue
quantum simulation in the presence of noise.
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All authors Gabriele Bressanini, Yue Ma, Hyukjoon Kwon, M.S. Kim
Quantum Physics
Below-threshold error reduction in single photons through photon distillation
F. H. B. Somhorst, J. Saied, N. Kannan et al. (+14 more)
Photonic
quantum computers use the bosonic statistics of
photons to construct, through
quantum interference, the large entangled states required for measurement-based
quantum computation. Therefore, any which-way information present in the
photons will degrade
quantum interference and introduce errors. While
quantum error correction can address such errors in principle, it is highly resource-intensive and operates with a low error threshold, requiring numerous high-quality optical components. We experimentally demonstrate scalable, optimal
photon distillation as a substantially more resource-efficient strategy to reduce indistinguishability errors in a way that is compatible with fault-tolerant operation.
Photon distillation is an intrinsically bosonic, coherent error-mitigation technique which exploits
quantum interference to project single
photons into purified internal states, thereby reducing indistinguishability errors at both a higher efficiency and higher threshold than
quantum error correction. We observe unconditional error reduction (i.e., below-threshold behaviour) consistent with theoretical predictions, even when accounting for noise introduced by the
distillation gate, thereby achieving actual net-gain error mitigation under conditions relevant for fault-tolerant
quantum computing. We anticipate
photon distillation will find uses in large-scale
quantum computers. We also expect this work to inspire the search for additional intrinsically bosonic error-reduction strategies, even for fault-tolerant architectures.
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All authors F. H. B. Somhorst, J. Saied, N. Kannan, B. Kassenberg, J. Marshall, M. de Goede, H. J. Snijders, P. Stremoukhov, A. Lukianenko, P. Venderbosch, T. B. Demille, A. Roos, N. Walk, J. Eisert, E. G. Rieffel, D. H. Smith, J. J. Renema
Quantum Physics
Universal Dilation of Linear Itô SDEs: Quantum Trajectories and Lindblad Simulation of Second Moments
Hsuan-Cheng Wu and Xiantao Li
We present a universal framework for simulating $N$-dimensional linear Itô
stochastic differential equations (SDEs) on
quantum computers with additive or multiplicative noises. Building on a
unitary dilation technique, we establish a rigorous mapping from the general linear SDEs \[ dX_t = A(t) X_t\,dt + \sum_{j=1}^J B_j(t)X_t\,dW_t^j \] to
stochastic Schrödinger equations (SSE) on a dilated
Hilbert space. Crucially, this
embedding is pathwise exact in that the classical solution is recovered as a projection of the dilated
quantum state for each fixed noise realization. We demonstrate that the resulting SSEs are {naturally implementable} on digital
quantum processors, where the
stochastic Wiener increments are encoded directly by preparing the ancillary
qubits. Exploiting this physical mapping, we develop two algorithmic strategies: (1) a trajectory-based approach that uses sequential weak measurements to realize efficient
stochastic integrators, including a second-order scheme, and (2) an ensemble-based approach that maps moment
evolution to a deterministic Lindblad
quantum master equation, enabling simulation without Monte Carlo sampling. We provide error bounds based on a
stochastic light-cone analysis and validate the framework with numerical experiments.
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Quantum Physics
Dynamical entanglement percolation with spatially correlated disorder
Lorenzo Cirigliano, Valentina Brosco, Claudio Castellano et al. (+3 more)
The distribution of
entanglement between the nodes of a
quantum network plays a fundamental role in
quantum information applications. In this work, we investigate the dynamics of a network of
qubits where each edge corresponds to an independent two-
qubit interaction. By applying tools from percolation theory, we study how
entanglement dynamically spreads across the network. We show that the interplay between
unitary evolution and spatially correlated disorder leads to a non-standard percolation phenomenology, significantly richer than uniform bond percolation and featuring hysteresis. A two-colour correlated bond percolation model, whose phase diagram is determined via numerical simulations and a mean-field theory, fully elucidates the physics behind this phenomenon.
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All authors Lorenzo Cirigliano, Valentina Brosco, Claudio Castellano, Simone Felicetti, Laura Pilozzi, Bernard van Heck
Quantum Physics
Generation of squeezed optical states via stored classical pulses in a Bose gas
Sevilay Sevinçli, Dennis Rätzel, Markus Krutzik et al. (+2 more)
We propose and analyze a scheme to generate squeezed light by storing a classical probe pulse in a Bose–Einstein condensate (BEC) and exploiting the nonlinear
evolution caused by atom–atom collisions during the storage time. A $\Lambda$-type optical
memory interface maps a chosen temporal probe mode onto a single phase-matched collective
spin wave; for a coherent input this prepares a tunable coherent
spin state of a two-component BEC, with its initial
spin orientation set by the stored mean excitation number and the phase relation between the probe and control fields. Collisional interactions during storage then implement one-axis-twisting dynamics and generate
spin squeezing in the atomic ensemble. We account for realistic loss and finite
memory and
retrieval efficiencies, and model readout as a single-mode beam-splitter mapping that transfers the atomic quadrature squeezing onto a propagating optical mode. We identify optimal storage times and predict that, under realistic conditions, several dB of squeezing can be transferred to the retrieved light.
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All authors Sevilay Sevinçli, Dennis Rätzel, Markus Krutzik, Mehmet Özgür Oktel, Mustafa Gündoğan
Quantum Physics
Sub-Planck structure quantification in non-Gaussian probability densities
Darren W. Moore, Vojtěch Švarc, Kratveer Singh et al. (+5 more)
Sub-Planck structures in non-Gaussian probability densities of phase space variables are pervasive in bosonic
quantum systems. They are almost universally present if the bosonic system evolves via nonlinear dynamics or nonlinear measurements. So far, identification and comparison of such structures remains qualitative. Here we provide a universally applicable and experimentally friendly method to identify, quantify and compare sub-Planck structures from directly measurable or estimated probability densities of single phase space variables. We demonstrate the efficacy of this method on experimental high order Fock states of a single-atom mechanical oscillator, showing provably finer sub-Planck structures as the Fock occupation increases despite the accompanying uncertainty increase in the
phonon, position, and momentum bases.
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All authors Darren W. Moore, Vojtěch Švarc, Kratveer Singh, Artem Kovalenko, Minh Tuan Pham, Ondřej Číp, Lukáš Slodička, Radim Filip
Quantum Physics
Breaking the Exponential: Decoherence-Driven Power-Law Spontaneous Emission in Waveguide Quantum Electrodynamics
Stefano Longhi
We investigate the spontaneous emission of a two-level system coupled to a photonic waveguide, showing that dynamical dephasing in the
photon modes profoundly alters the decay law. In the absence of dephasing, the emitter displays conventional exponential decay followed by a long-time power-law tail – observable only at extremely low survival probabilities. Strikingly, when dephasing is introduced, a robust power-law decay emerges already at short times, driven by
photon diffusion in the dynamically disordered environment rather than spectral edge effects. These results reveal a novel, decoherence-induced mechanism for non-exponential spontaneous emission in waveguide QED platforms.
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Quantum Physics
Optimally driving multi-photon transitions in the perturbative single-mode regime
Frieder Lindel, Stefan Yoshi Buhmann, Andreas Buchleitner et al. (+1 more)
The rate of $m$-
photon transitions in matter, induced by an incident light field, depends on the field's $m$th order coherence function. Consequently, the coherence properties of the light field may be shaped to increase the rate of multi-
photon transitions. Here, we determine the optimal state of a weak fixed-intensity, narrow-band incident light field, with a restricted maximal
photon number, that optimally drives $m$-
photon transitions in the case of a short-lived atomic multilevel system. We show that, in this case, no
quantum properties of the light field need to be exploited, but that classical mixtures of coherent states are optimal.
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All authors Frieder Lindel, Stefan Yoshi Buhmann, Andreas Buchleitner, Edoardo G. Carnio
Quantum Physics
On the robustness of Quantum Phase Estimation to compute ground properties of many-electron systems
Wassil Sennane and Jérémie Messud
We propose an analysis of the
Quantum Phase Estimation (QPE)
algorithm applied to many-electron systems by investigating its free parameters such as the time step, number of phase
qubits, initial state preparation, number of measurement shots, and other parameters related to the
unitary operators implementation. A deep understanding of these parameters and their impact on QPE probability of success and precision of the results is important to pave the way towards more automation of QPE applied to predictive computational chemistry and material science. We here explicit a constructive method to set the QPE free parameters for ground energy estimation and ground state projection, gathering disseminated results from previous works, refining these results and developing new conditions for achieving target performance. We detail the impact of the QPE `blurring function', related to discretization effects, and propose a method to overcome corresponding pathologies. We finally demonstrate that, using the conditions gathered here, the complexity of the Trotterized version of QPE tends to depend mostly on physical system properties and weakly on the number of phase
qubits. Various numerical results illustrate the impact of QPE free parameters on success probability and discretization effects. The impact of Trotterization and other features on the precision of the results are illustrated by first numerical simulations on the H2 molecule, that allows us to derive useful insights.
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