arXiv subjects

Paul M. Alsing

Publications and source records attributed to Paul M. Alsing.

At least 19 recordsLinked to original sources

arXiv2026

From Quantum-Mechanical Acceleration Limits to Upper Bounds on Fluctuation Growth of Observables in Unitary Dynamics

Recently, the notion of a quantum acceleration limit has been proposed for any unitary time evolution of quantum systems governed by arbitrary nonstationary Hamiltonians. This limit articulates that the rate of change over time of the standard deviation of the Hamiltonian operator representing the acceleration of quantum evolution within projective Hilbert space is constrained by the standard deviation of the time-derivative of the Hamiltonian. In this paper, we extend our earlier findings to encompass any observable A within the framework of unitary quantum dynamics, leading to the inequality. This relationship signifies that the speed of the standard deviation of any observable is limited by the standard deviation of its associated velocity-like observable. Finally, for pedagogical purposes, we illustrate the relevance of our inequality by providing clear examples. We choose suitable observables related to the unitary dynamics of two-level quantum systems, as well as a harmonic oscillator within a finite-dimensional Fock space.

quant-ph↗

arXiv2026

Lattice Quantization of Free Fermions without Doublers

We present a method to quantize free fermions which eliminates the doublers when implemented on the lattice in any number of dimensions and in the $m=0$ limit. The elimination of doublers is achieved by combining a second-order description of fermions, with the tools associated with non-Hermitian Hamiltonians. We identify a new Pseudo-Hermitian symmetry of the second-order fermion equation, and we identify the associated $U(1)$ symmetry which will become charge when shifted to a local gauge theory. We validated the methods numerically.

hep-lat↗

arXiv2026

WKB-like approach to the Unruh temperature for arbitrary acceleration

In this work we study the Unruh temperature as arising from tunneling through a barrier for an observer in flat Minkowski spacetime with arbitrary acceleration $a(t)$. For the defining case of constant acceleration $a(t) = a_0$, the Unruh temperature (W. Unruh, Phys. Rev. D 14, 870 (1976)) is given by $k_b\,T_U =\tfrac{\hbar\,a_0}{2\,π\,c}$. Extending the work of de Gill et al. (A. de Gill, D. Singleton, V. Akhmedova and T. Pilling, Am. J. Phys. 78, 685 (2010)) we generalize the gravitational WKB approach to derive the Unruh temperature for arbitrary acceleration. We show that the often employed Schwarzschild-like form of the flat metric is not appropriate for the WKB calculation with an arbitrary $a(t)$, and instead derive a generalized Unruh temperature for the generalized Rindler metric where $a_0\to a(t)$. We derive a generalization of the Rindler coordinates appropriate for arbitrary $a(t)$, and stress the importance of the role of the integrated acceleration $χ(t) = \int^t dt'\,a(t')$, which can also act as a temporal coordinate. We explore several non-trivial examples of $a(t)$ and their generalized Unruh temperatures. We additionally develop an approximation to the Unruh temperature for small deviations away from constant acceleration by the standard approach of considering the negative frequency content of a purely positive frequency plane wave of an inertial observer, as measured by the co-moving arbitrarily accelerated observer. Lastly, we develop and explicit coordinate transformation between the arbitrarily accelerated observer and conformal coordinates, where the plane wave structure of the solutions of the wave equation is readily transparent, and analogous to the form for the inertial observer.

gr-qc↗

arXiv2026

Inertial-to-Rindler Coordinates, with applications to the Twin Paradox, Radar Time and the Unruh Temperature

In this work we formulate a two-parameter family of transformations in flat Minkowksi spacetime that smoothly interpolates between motion with constant initial/final velocity (inertial coordinates), and with constant acceleration (Rindler coordinates \cite{Rindler:1956}), which we term Inertial-to-Rindler (I2R) coordinates. We revisit the Twin ``Paradox" and show how the new I2R coordinates justify the ``immediate-" and ``gradual-turnaround" scenarios discussed in many texbooks and articles. We also examine the radar time formulation of hypersurfaces of simultaneity by Dolby and Gull \cite{Dolby_Gull:2001} for these new coordinates as we transition from zero to uniform acceleration. Finaly we re-examine the negative frequency content of a purely positive frequency Minkowski plane wave as observed by the I2R observer, and derive perturbative corrections to the Unruh \cite{Unruh:1976} temperature for the two cases of initial/final velocities slightly greater than zero, and slightly less than the speed of light - the latter of which characterizes constant acceleration motion. We argue for a proposed velocity-dependent generalization of the Unruh temperature that smoothly varies from zero at zero-acceleration, to the standard form at constant acceleration.

gr-qc↗

arXiv2026

Quantum Optical Inspired Models for Unitary Black Hole Evaporation

In this work, we describe optically inspired models for unitary black hole (BH) evaporation. The goal of these models are (i) to be operationally simple, (ii) approximately preserve the thermal nature of the emitted Hawking Radiation (HR), and (iii) attempt to reproduce the Page Curve that purports that information flows forth from the BH when it has evaporated to approximately half its initial mass. We concentrate on modeling the BH as a single mode squeezed state successively interacting, by means of beam splitters and squeezers, with vacuum modes near the horizon, giving rise to entangled pairs representing the external Hawking radiation and its partner particle inside the horizon. Since all states and operations are Gaussian throughout, we use a symplectic formalism to track the evolution of the composite system through the evolving means and variances of their quadrature operators. This allows us to easily compute correlations and entanglement between the BH and the HR, as well as calculate correlations between the BH at early and late times.

gr-qc↗

arXiv2026

Multiphoton Interference with a symmetric SU(N) beam splitter and the generalization of the extended Hong-Ou-Mandel effect

We examine multiphoton interference with a symmetric $SU(N)$ beam splitter $S_N$, an extension of features of the $SU(2)$ 50/50 beam splitter extended Hong-Ou-Mandel (eHOM) effect, whereby one obtains a zero amplitude (probability) for the output coincidence state (defined by equal number of photons $n/N$ in each output port), when a total number $n$ of photons impinges on the $N$-port device. These are transitions of the form $|n_1,n_2,\ldots,n_N\rangle\overset{S_N}{\to}|n/N\rangle^{\otimes N}$, where $n=\sum_{i=1}^N n_i$, which generalize the Hong-Ou-Mandel (HOM) effect $|1,1\rangle \overset{S_2}{\to}|1,1\rangle $, the eHOM effect $|n_1,n_2\rangle \overset{S_2}{\to}|\tfrac{n_1+n_2}{2},\tfrac{n_1+n_2}{2}\rangle $, and the generalized HOM effect (gHOM) $|1\rangle^{\otimes N}\overset{S_N}{\to}|1\rangle^{\otimes N}$, which have previously been studied in the literature. The emphasis of this work is on illuminating how the overall destructive interference occurs in separate groups of destructive interferences of sub-amplitudes of the total zero amplitude. We develop symmetry properties for the generalized eHOM effect (geHOM) $|n_1,n_2,\ldots,n_N\rangle\overset{S_N}{\to}|n/N\rangle^{\otimes N}$ involving a zero amplitude governed by Perm($Λ$)=0, for an appropriately constructed matrix $Λ(S_N)$ built from the matrix elements of $S_N$. We develop an analytical constraint equation for Perm$(Λ)$ for arbitrary $N$ that allows us to determine when it is zero. We generalize the SU(2) beam splitter feature of central nodal line (CNL), which has a zero diagonal along the output probability distribution when one of the input states is of odd parity (containing only odd number of photons), to the general case of $N = 2 * N'$ where $N'\in odd$.

quant-ph↗

arXiv2025

Upper Bounds on Fluctuation Growths of Observables in Open Quantum Systems

The upper bounds for the rate of fluctuation growth of an observable in both open and closed quantum systems have been studied actively recently. In our recent work we showed that the rate of fluctuation growth for an observable in a closed quantum system is upper bounded by the fluctuation of its corresponding velocity-like observable. That bound also indicated a tradeoff between the time derivatives of the mean and the standard deviation. In this paper we will look at open quantum systems in two cases. For the first case we find the generator of evolution for an open system employing both the Taylor expansion and the standard time-ordered evolution via the Dyson series, while in the second case we consider no specific information about the evolution of the system. We then find the rate of fluctuation growth in each case. Comparing the upper bounds for each case and considering the upper bound found for a closed system suggest that including more details by separating the contributions of the system and state dynamics seems to result in looser bounds for the rate of fluctuation growth.

quant-ph↗

arXiv2025

Telecommunications fiber-optic and free-space quantum local area networks at the Air Force Research Laboratory

As quantum computing, sensing, timing, and networking technologies mature, quantum network testbeds are being deployed across the United States and around the world. To support the Air Force Research Laboratory (AFRL)'s mission of building heterogeneous quantum networks, we report on the development of Quantum Local Area Networks (QLANs) operating at telecommunications-band frequencies. The multi-node, reconfigurable QLANs include deployed optical fiber and free-space links connected to pristine laboratory environments and rugged outdoor test facilities. Each QLAN is tailored to distinct operating conditions and use cases, with unique environmental characteristics and capabilities. We present network topologies and in-depth link characterization data for three such networks. Using photonic integrated circuit-based sources of entangled photons, we demonstrate entanglement distribution of time-energy Bell states across deployed fiber in a wooded environment. The high quality of the entanglement is confirmed by a Clauser-Horne-Shimony-Holt inequality violation of $S=2.717$, approaching the theoretical maximum of $S=2.828$. We conclude with a discussion of future work aimed at expanding QLAN functionality and enabling entanglement distribution between heterogeneous matter-based quantum systems, including superconducting qubits and trapped ions. These results underscore the practical viability of field-deployable, qubit-agnostic quantum network infrastructure.

quant-ph↗

arXiv2025

Microring resonator-based photonic circuit for faithfully heralding NOON states

We have designed a Micro-Ring Resonator (MRR) based device that allows for the post-selection of high order NOON states via heralding. NOON states higher than $N=2$ cannot be generated deterministically. By tuning the coupling parameters of the device we can minimize the amplitudes of the 'accidental' states to maximize the probability of obtaining the NOON state upon a successful heralding event. Our device can produce a 3-photon NOON state output with 100% certainty upon a successful heralding detection, which occurs with probability $\frac{8}{27}$ for optimal tunable device parameters. A successful heralding event allows for non-destructive time of flight tracking of the NOON state thus establishing a significantly enhanced level of engineering control for integration of the NOON state into scalable systems for quantum sensing and metrology. We further discuss extensions of our technique to even higher NOON states having $N=4,5$.

quant-ph↗

arXiv2025

Hong-Ou-Mandel Comb and Switch using parallel chains of non-identical Micro-Ring Resonators

Micro-Ring Resonators (MRRs) allow us to access the Hong-Ou-Mandel (HOM) effect at a variety of tunable parameter combinations along exact analytic solutions. This higher-dimensional space of parameters for which the HOM effect occurs constitutes what is known as a Hong-Ou-Mandel manifold (HOMM). Using a parallel series of non-identical MRRs and changing relative round-trip phase shifts between MRRs allows for the manipulation of the wavelength locations of the HOM effect. Through clever design and fabrication, we can mold the HOMM to place multiple HOM effects, or lack thereof, precisely at desired locations in wavelength. In this paper we discuss how to adjust non-identical MRR parameters to change the resulting HOMM. We also promote example designs that exhibit advantageous HOMM structures, and highlight some of the diverse possibilities that can be accessed with different circuit design. Our main examples are: 1) a wavelength division multiplexer example that matches the HOM effect locations with the already established channels to integrate with a classical communication network and 2) a HOM-based entanglement switch that allows for the rapid switching between 2-photon NOON state outputs and completely separable single photon outputs.

physics.optics↗

arXiv2025

Black Hole Waterfall: a unitary phenomenological model for black hole evaporation with Page curve

We present a unitary phenomenological model for black hole evaporation based on the analogy of the laboratory process of spontaneous parametric down conversion (SPDC) when the black hole (pump) is allowed to deplete to zero mass. The model incorporates an additional new feature that allows for the interior Hawking partner-particles (idlers) behind the horizon to further generate new Hawking particle pairs of lower energy, one of which remains behind the horizon, and the other that adds to the externally emitted Hawking radiation (signals) outside the horizon. This model produces a Page curve for the evolution of the reduced density matrices for the evaporating black hole internal degrees of freedom entangled with the generated Hawking radiation pairs entangled across the horizon. The Page curve yields an entropy that rises at early times during the evaporation process as Hawking pairs are generated, reaches a peak midway through the evolution, and then decays to zero upon complete evaporation of the black hole. The entire system remains in a pure state at all times undergoing unitary (squeezed state) evolution, with the initial state of the black hole modeled as a bosonic Fock state of large, but finite number $n_{p0}$ of particles. For the final state of the system, the black hole reaches the vacuum state of zero mass, while the external Hawking radiation carries away the total energy of the initial black hole. Inside the horizon there remains $n_{p0}$ Hawking partner-particles of vanishingly small total energy, reminiscent of the "soft-hair" (zero energy) qubit model of Hotta, Nambu and Yamaguchi, but now from a Hamiltonian for squeezed state generation perspective. The model presented here can be readily extended to encompass arbitrary initial pure states for the black hole, and in falling matter.

gr-qc↗

arXiv2025

Deviations from Geodesic Evolutions and Energy Waste on the Bloch Sphere

In optimal quantum-mechanical evolutions, motion can occur along non-predetermined paths of shortest length in an optimal time. Alternatively, optimal evolutions can happen along predefined paths with no waste of energy resources and 100% speed efficiency. Unfortunately, realistic physical scenarios typically result in less-than-ideal evolutions. In this paper, we study different families of sub-optimal qubit Hamiltonians, both stationary and time-varying, for which the so-called geodesic efficiency and the speed efficiency of the corresponding quantum evolutions are less than one. Furthermore, after proposing an alternative hybrid efficiency measure constructed out of the two previously mentioned efficiency quantifiers, we provide illustrative examples where the average departures from time-optimality and 100% speed efficiency are globally captured over a limited time period. In particular, thanks to this hybrid measure, quantum evolutions are partitioned in four categories: Geodesic unwasteful, nongeodesic unwasteful, geodesic wasteful and, lastly, nongeodesic wasteful. Finally, we discuss Hamiltonians specified by magnetic field configurations, both stationary and nonstationary, yielding optimal hybrid efficiency (that it, both time-optimality and 100% speed efficiency) over a finite time interval.

quant-ph↗

arXiv2025

Frequency auto-homogenization using group-velocity-matched downconversion

With the stability of integrated photonics at network nodes and the advantages of photons as flying qubits, photonic quantum information processing (PQIP) makes quantum networks increasingly scalable. However, scaling up PQIP requires the preparation of many identical single photons which is limited by the spectral distinguishability of integrated single-photon sources due to variations in fabrication or local environment. To address this, we introduce frequency auto-homogenization via group-velocity-matched downconversion to remove spectral distinguishability in varying quantum emitters. We present our theory using $χ^{(2)}$ quantum frequency conversion and show proof-of-principle data in a free-space optical setup.

quant-ph↗

arXiv2025

Principles for Optimizing Quantum Transduction in Piezo-Optomechanical Systems

Two-way microwave-optical quantum transduction is essential to connecting distant superconducting qubits via optical fiber, and to enable quantum networking at a large scale. In Blésin, Tian, Bhave, and Kippenberg's article, ``Quantum coherent microwave-optical transduction using high overtone bulk acoustic resonances" (Phys. Rev. A, 104, 052601 (2021)), they lay out a two-way quantum transducer converting between microwave photons and telecom-band photons by way of an intermediary GHz-band phonon mode utilizing piezoelectric and optomechanical interactions respectively (and are the first to work out the quantum piezoelectric coupling). In this work, we examine both the piezoelectric, and optomechanical interactions from first principles, and together with the evanescent coupling between optical modes, discuss what parameters matter most in optimizing this kind of quantum transducer. For its additional utility, we have also compiled a table of relevant properties of optical materials that may be used as elements in transducers.

quant-ph↗

arXiv2025

An examination of the extended Hong-Ou-Mandel effect and considerations for experimental detection

In recent works we have explored a multi-photon extension of the celebrated two-photon Hong-Ou-Mandel (HOM) effect in which the quantum amplitudes for a two-photon input to a lossless, balanced 50:50 beamsplitter (BS) undergoes complete destructive interference. In the extended Hong-Ou-Mandel (eHOM) effect the multi-photon scattering of photons from the two input ports to the two output ports of the BS for Fock number basis input states (FS) $|n,m\rangle_{12}$ exhibit complete destructive interference pairwise within the quantum amplitudes containing many scattering components, generalizing the two-photon HOM effect. This has profound implications for arbitrary bipartite photonic input states constructed from such basis states: if the input state to one input port of the BS is of odd parity, i.e. constructed from only of odd numbers of photons, then regardless of the input state to the second 50:50 BS port, there will be a central nodal line (CNL) of zeros in the joint output probability distribution along the main diagonal for coincidence detection. The first goal of this present work is to show diagrammatically how the extended HOM effect can be seen as a succession of multi-photon HOM effects when the latter is viewed as a pairwise cancellation of mirror image scattering amplitudes. The second goal of this work is to explore considerations for the experimental realization of the extended Hong-Ou-Mandel effect. We examine the case of a single photon interfering with a coherent state (an idealized laser) on a balanced 50:50 beamsplitter and consider prospects for experimental detection of the output destructive interference by including additional effects such as imperfect detection efficiency, spatio-temporal mode functions, and time delay between the detected output photons.

quant-ph↗

arXiv2025

Curvature of Quantum Evolutions for Qubits in Time-Dependent Magnetic Fields

In the geometry of quantum-mechanical processes, the time-varying curvature coefficient of a quantum evolution is specified by the magnitude squared of the covariant derivative of the tangent vector to the state vector. In particular, the curvature coefficient measures the bending of the quantum curve traced out by a parallel-transported pure quantum state that evolves in a unitary fashion under a nonstationary Hamiltonian that specifies the Schrodinger evolution equation. In this paper, we present an exact analytical expression of the curvature of a quantum evolution for a two-level quantum system immersed in a time-dependent magnetic field. Specifically, we study the dynamics generated by a two-parameter nonstationary Hermitian Hamiltonian with unit speed efficiency. The two parameters specify the constant temporal rates of change of the polar and azimuthal angles used in the Bloch sphere representation of the evolving pure state. To better grasp the physical significance of the curvature coefficient, showing that the quantum curve is nongeodesic since the geodesic efficiency of the quantum evolution is strictly less than one and tuning the two Hamiltonian parameters, we compare the temporal behavior of the curvature coefficient with that of the speed and the acceleration of the evolution of the system in projective Hilbert space. Furthermore, we compare the temporal profile of the curvature coefficient with that of the square of the ratio between the parallel and transverse magnetic field intensities. Finally, we discuss the challenges in finding exact analytical solutions when extending our geometric approach to higher-dimensional quantum systems that evolve unitarily under an arbitrary time-dependent Hermitian Hamiltonian.

quant-ph↗

arXiv2024

Complexity of Quantum-Mechanical Evolutions from Probability Amplitudes

We study the complexity of both time-optimal and time sub-optimal quantum Hamiltonian evolutions connecting arbitrary source and a target states on the Bloch sphere equipped with the Fubini-Study metric. This investigation is performed in a number of steps. First, we describe each unitary Schrödinger quantum evolution by means of the path length, the geodesic efficiency, the speed efficiency, and the curvature coefficient of its corresponding dynamical trajectory linking the source state to the target state. Second, starting from a classical probabilistic setting where the so-called information geometric complexity can be employed to describe the complexity of entropic motion on curved statistical manifolds underlying the physics of systems when only partial knowledge about them is available, we transition into a deterministic quantum setting. In this context, after proposing a definition of the complexity of a quantum evolution, we present a notion of quantum complexity length scale. In particular, we discuss the physical significance of both quantities in terms of the accessed (i.e., partial) and accessible (i.e., total) parametric volumes of the regions on the Bloch sphere that specify the quantum mechanical evolution from the source to the target states. Third, after calculating the complexity measure and the complexity length scale for each one of the two quantum evolutions, we compare the behavior of our measures with that of the path length, the geodesic efficiency, the speed efficiency, and the curvature coefficient. We find that, in general, efficient quantum evolutions are less complex than inefficient evolutions. However, we also observe that complexity is more than length. Indeed, longer paths that are sufficiently bent can exhibit a behavior that is less complex than that of shorter paths with a smaller curvature coefficient.

quant-ph↗

arXiv2024

The Hong-Ou-Mandel effect is really odd

When quantum state amplitudes interfere, surprising non-classical features emerge which emphasis the roles of indistinguishability and discreteness in quantum mechanics. A famous example in quantum optics is the Hong Ou Mandel interference effect,a major ingredient in current quantum information processing using photonics. Traditionally the HOM features interference between amplitudes for two one-photon number states. Surprisingly, interference can be manifested when one amplitude represents that most classical of light field states, the coherent state, provided the partner state is non-classical (eg a single photon state or an odd photon number state). Imposing such nonclassical features on an otherwise classical state is the focus of this article. Recently, the HOM effect has been generalized to the multi-photon case, termed the extended HOM effect by the authors.The implication of the extended HOM effect is that if an odd parity state, comprising only odd numbers of photons, enters one input port of a 50:50 beam splitter, then regardless of the state entering the other input port, be it pure or mixed, there will no output coincident counts. In this work, we explain the extended HOM as arising from a sequence of pairwise HOM-like complete destructive interferences occurring simultaneously in the multicomponent amplitude for the output coincidence counts. We first demonstrate this diagrammatically in order to build physical intuition, before developing a general analytical proof. We then examine the case of a single photon interacting with a coherent state (and idealized laser), and consider prospects for experimental detection by including the effect of imperfect detection efficiency. This work highlights the importance of the non-classicality of light, and in particular the interference effects stemming from the discreteness of photon quanta.

quant-ph↗