Symplectic Phase Space Research Articles

Pointillisme à la Signac and Construction of a Quantum Fiber Bundle Over Convex Bodies

We use the notion of polar duality from convex geometry and the theory of Lagrangian planes from symplectic geometry to construct a fiber bundle over ellipsoids that can be viewed as a quantum-mechanical substitute for the classical symplectic phase space. The total space of this fiber bundle consists of geometric quantum states, products of convex bodies carried by Lagrangian planes by their polar duals with respect to a second transversal Lagrangian plane. Using the theory of the John ellipsoid we relate these geometric quantum states to the notion of “quantum blobs” introduced in previous work; quantum blobs are the smallest symplectic invariant regions of the phase space compatible with the uncertainty principle. We show that the set of equivalence classes of unitarily related geometric quantum states is in a one-to-one correspondence with the set of all Gaussian wavepackets. We emphasize that the uncertainty principle appears in this paper as geometric property of the states we define, and is not expressed in terms of variances and covariances, the use of which was criticized by Hilgevoord and Uffink.

Symplectic Polar Duality, Quantum Blobs, and Generalized Gaussians

We apply the notion of polar duality from convex geometry to the study of quantum covariance ellipsoids in symplectic phase space. We consider in particular the case of “quantum blobs” introduced in previous work; quantum blobs are the smallest symplectic invariant regions of the phase space compatible with the uncertainty principle in its strong Robertson–Schrödinger form. We show that these phase space units can be characterized by a simple condition of reflexivity using polar duality, thus improving previous results. We apply these geometric constructions to the characterization of pure Gaussian states in terms of partial information on the covariance ellipsoid, which allows us to formulate statements related to symplectic tomography.

Hydrodynamic interpretation of generic squeezed coherent states: A kinetic theory

The hydrodynamic interpretation of quantum mechanics treats a system of particles in an effective manner which allows one to study the system in a statistical fashion. In this work, we investigate squeezed coherent states within the hydrodynamic interpretation. The Hamiltonian operator in question is time dependent, n-dimensional and in quadratic order. We start by deriving a phase space Wigner probability distribution and an associated equilibrium entropy for the squeezed coherent states. Then, we decompose the joint phase space distribution into two portions: A marginal position distribution and a momentum distribution that is conditioned on the post-selection of positions. Our conditionally averaged momenta are shown to be equal to the Bohm’s momenta whose connection to the weak measurements is already known. We also keep track of the corresponding classical system evolution by identifying shear, magnification and rotation components of the symplectic phase space dynamics. This allows us to pinpoint which portion of the underlying classical motion appears in which quantum statistical concept. We show that our probability distributions satisfy the Fokker–Planck equations exactly and they can be used to decompose the equilibrium entropy into the missing information in positions and in momenta as in the Sackur–Tetrode entropy of the classical kinetic theory. Eventually, we define a quantum pressure, a quantum temperature and a quantum internal energy which are related to each other in the same fashion as in the classical kinetic theory. We show that the quantum potential incorporates the kinetic part of the internal energy and the fluctuations around it. This allows us to suggest a quantum conditional virial relation. In the end, we show that the kinetic internal energy is linked to the fractional Fourier transformer part of the underlying classical dynamics similar to the case where the energy of a quantum oscillator is linked to its Maslov index.

The Equiareal Archimedean Synchronization Method of the Quantum Symplectic Phase Space: I. Spinorial Amplitudes, Transition Probability, and Areal Measure of Time

The Equiareal Archimedean Synchronization Method of the Quantum Symplectic Phase Space: I. Spinorial Amplitudes, Transition Probability, and Areal Measure of Time

Hydrodynamic Interpretation of Generic Squeezed Coherent States: A Kinetic Theory

The hydrodynamic interpretation of quantum mechanics treats a system of particles in an effective manner. In this work, we investigate squeezed coherent states within the hydrodynamic interpretation. The Hamiltonian operator in question is time dependent, n-dimensional and in quadratic order. We start with deriving a phase space Wigner probability distribution and an associated equilibrium entropy for the squeezed coherent states. Then, we decompose the joint phase space distribution into two portions: a marginal position distribution and a momentum distribution that is conditioned on the post-selection of positions. Our conditionally averaged momenta is shown to be equal to the Bohm's momenta whose connection to the weak measurements is already known. We also keep track of the corresponding classical system evolution by identifying shear, magnification and rotation components of the symplectic phase space dynamics. This allows us to pinpoint which portion of the underlying classical motion appears in which quantum statistical concept. We show that our probability distributions satisfy the Fokker-Planck equations exactly. They can be used to decompose the equilibrium entropy into the missing information in positions and in momenta as in the Sackur-Tetrode entropy of the classical kinetic theory. Eventually, we define a quantum pressure, a quantum temperature and a quantum internal energy which are related to each other in the same fashion as in the classical kinetic theory. We show that the quantum potential incorporates the kinetic part of the internal energy and the fluctuations around it. This allows us to suggest a quantum conditional virial relation. In the end, we show that the kinetic internal energy is linked to the fractional Fourier transformer part of the underlying classical dynamics similar to the case where the energy of a quantum oscillator is linked to its Maslov index.

A Hamiltonian mechanics framework for charge particle optics in straight and curved systems

Charged particle optics, the description of particle trajectories in the vicinity of some optical axis, describe the imaging properties of particle optics devices. Here, we present a complete and compact description of charged particle optics employing perturbative expansion of Hamiltonian mechanics. The derived framework allows the straightforward computation of transversal and longitudinal (chromatic) properties of static and dynamic optical devices with straight and curved optical axes. It furthermore gives rise to geometric integration schemes preserving the symplectic phase space structure and pertaining Lagrange invariants, which may be employed to derive analytic approximations of aberration coefficients and efficient numerical trajectory solvers.

Squeezed out-of-time-order correlator and cosmology

Exponential growth in the out-of-time-order correlator (OTOC) is an important potential signature of quantum chaos. The OTOC is quite simple to calculate for squeezed states, whose applications are frequently found in quantum optics and cosmology. We find that the OTOC for a generic highly squeezed quantum state is exponentially large, suggesting that highly squeezed states are "primed" for quantum chaos. A quantum generalization of the classical symplectic phase space matrix can be used to extract the quantum Lyapunov spectrum, and we find this better captures the exponential growth of squeezed states for all squeezing angles compared to any single OTOC. By describing cosmological perturbations in the squeezed state language, we are able to apply our calculations of the OTOC to arbitrary expanding and contracting backgrounds with fixed equation of state. We find that only expanding de Sitter backgrounds support an exponentially growing OTOC at late times, with a putative Lyapunov exponent consistent with other calculations. While the late-time behavior of the OTOC for other cosmological backgrounds appears to change depending on the equation of state, we find that the quantum Lyapunov spectrum shows some universal behavior: the OTOC grows proportional to the scale factor for perturbation wavelengths larger than the cosmological Hubble horizon.

Symplectic coarse-grained classical and semclassical evolution of subsystems: New theoretical approach

We study the classical and semiclassical time evolutions of subsystems of a Hamiltonian system; this is done using a generalization of Heller’s thawed Gaussian approximation introduced by Littlejohn. The key tool in our study is an extension of Gromov’s “principle of the symplectic camel” obtained in collaboration with Dias, de Gosson, and Prata [arXiv:1911.03763v1 [math.SG] (2019)]. This extension says that the orthogonal projection of a symplectic phase space ball on a phase space with a smaller dimension also contains a symplectic ball with the same radius. In the quantum case, the radii of these symplectic balls are taken equal to ℏ and represent the ellipsoids of minimum uncertainty, which we called “quantum blobs” in previous work.

Periodic fourth-order cubic NLS: Local well-posedness and non-squeezing property

In this paper, we consider the cubic fourth-order nonlinear Schrödinger equation (4NLS) under the periodic boundary condition. We prove two results. One is the local well-posedness in Hs(T) with −1/3≤s<0 for the Cauchy problem of the Wick ordered 4NLS. The other one is the non-squeezing property for the flow map of 4NLS in the symplectic phase space L2(T). To prove the former we used the ideas introduced in [36] and [27], and to prove the latter we used the ideas in [8].

Symplectic non-squeezing for the cubic nonlinear Klein–Gordon equation on [formula omitted

We consider the periodic defocusing cubic nonlinear Klein–Gordon equation in three dimensions in the symplectic phase space H12(T3)×H−12(T3). This space is at the critical regularity for this equation, and in this setting there is no global well-posedness nor any uniform control on the local time of existence for arbitrary initial data. We prove a local-in-time non-squeezing result and a conditional global-in-time result which states that uniform bounds on the Strichartz norms of solutions imply global-in-time non-squeezing. As an application of the conditional result, we conclude non-squeezing for certain subsets of the phase space. The proofs rely on several approximation results for the flow, which we obtain using a combination of probabilistic and deterministic techniques.

Geometry of Discrete-Time Spin Systems

Classical Hamiltonian spin systems are continuous dynamical systems on the symplectic phase space $(S^2)^n$. In this paper we investigate the underlying geometry of a time discretization scheme for classical Hamiltonian spin systems called the spherical midpoint method. As it turns out, this method displays a range of interesting geometrical features, that yield insights and sets out general strategies for geometric time discretizations of Hamiltonian systems on non-canonical symplectic manifolds. In particular, our study provides two new, completely geometric proofs that the discrete-time spin systems obtained by the spherical midpoint method preserve symplecticity. The study follows two paths. First, we introduce an extended version of the Hopf fibration to show that the spherical midpoint method can be seen as originating from the classical midpoint method on $T^*\mathbf{R}^{2n}$ for a collective Hamiltonian. Symplecticity is then a direct, geometric consequence. Second, we propose a new discretization scheme on Riemannian manifolds called the Riemannian midpoint method. We determine its properties with respect to isometries and Riemannian submersions and, as a special case, we show that the spherical midpoint method is of this type for a non-Euclidean metric. In combination with K\"ahler geometry, this provides another geometric proof of symplecticity.

On the symplectic phase space of K\lowercase{d}V

AbstractWe prove that the Birkhoff map Ω for KdV constructed on H −10 (T) canbe interpolated between H −10 (T) and L 2 (T). In particular, the symplecticphase space H 1/20 (T) can be described in terms of Birkhoff coordinates. 1 Introduction In [12] it is shown that the Birkhoff map for the Korteweg - de Vries equation(KdV), on the circle T := R/Z, introduced and studied in detail in [9, 6] can beanalytically extended to an analytic diffeomorphismΩ : H −10 (T) → h −1/2 from the Sobolev space of distributions H −10 (T) (dual of H 10 (T)) to the Hilbertspace of sequences h −1/2 where for any α ∈ R,h α := {z = (x k ,y k ) k≥1 | kzk α < ∞},withkzk α :=X k≥1 k 2α (x 2k +y 2k ) 1/2 .In this paper we show that Ω can be interpolated between H −10 (T) and L 20 (T).Theorem 1. For any −1 ≤ α ≤ 0 , Ω| H α0 (T) : H α0 (T) → h α+1/2 is a real analytic diffeomorphism. As an application of Theorem 1 we characterize the regularity of a potentialq ∈ H −1 (T) in terms of the decay of the gap lengths (γ k

Hamiltonian dynamics on the symplectic extended phase space for autonomous and non-autonomous systems

We will present a consistent description of Hamiltonian dynamics on the ``symplectic extended phase space'' that is analogous to that of a time-\underline{in}dependent Hamiltonian system on the conventional symplectic phase space. The extended Hamiltonian $H_{1}$ and the pertaining extended symplectic structure that establish the proper canonical extension of a conventional Hamiltonian $H$ will be derived from a generalized formulation of Hamilton's variational principle. The extended canonical transformation theory then naturally permits transformations that also map the time scales of original and destination system, while preserving the extended Hamiltonian $H_{1}$, and hence the form of the canonical equations derived from $H_{1}$. The Lorentz transformation, as well as time scaling transformations in celestial mechanics, will be shown to represent particular canonical transformations in the symplectic extended phase space. Furthermore, the generalized canonical transformation approach allows to directly map explicitly time-dependent Hamiltonians into time-independent ones. An ``extended'' generating function that defines transformations of this kind will be presented for the time-dependent damped harmonic oscillator and for a general class of explicitly time-dependent potentials. In the appendix, we will reestablish the proper form of the extended Hamiltonian $H_{1}$ by means of a Legendre transformation of the extended Lagrangian $L_{1}$.

Quantum groups and deformation quantization: Explicit approaches and implicit aspects

Deformation quantization, which gives a development of quantum mechanics independent of the operator algebra formulation, and quantum groups, which arose from the inverse scattering method and a study of Yang–Baxter equations, share a common idea abstracted earlier in algebraic deformation theory: that algebraic objects have infinitesimal deformations which may point in the direction of certain continuous global deformations, i.e., “quantizations.” In deformation quantization the algebraic object is the algebra of “observables” (functions) on symplectic phase space, whose infinitesimal deformation is the Poisson bracket and global deformation a “star product,” in quantum groups it is a Hopf algebra, generally either of functions on a Lie group or (often its dual in the topological vector space sense, as we briefly explain) a completed universal enveloping algebra of a Lie algebra with, for infinitesimal, a matrix satisfying the modified classical Yang–Baxter equation (MCYBE). Frequently existence proofs are known but explicit formulas useful for physical applications have been difficult to extract. One success here comes from “universal deformation formulas” (UDFs), expressions built from a Lie algebra which deform any algebra on which the Lie algebra operates as derivations. The most famous of these is the Moyal product, a special case of a class in which the Lie algebra is Abelian. Another comes from recognition that the Belavin–Drinfel’d solutions to the MCYBE are, in fact, infinitesimal deformations for which, in the case of the special linear groups, it is possible to give explicit formulas for the corresponding quantum Yang–Baxter equations. This review paper discusses, necessarily in brief, these and related topics, including “twisting” as a form of UDF and finding formulas for “preferred deformations” of Hopf algebras in which the multiplication or comultiplication is rigid and must be preserved in the course of deformation.

Quantum magnetic algebra and magnetic curvature

The symplectic geometry of the phase space associated with a charged particle is determined by the addition of the Faraday 2-form to the standard structure on the Euclidean phase space. In this paper we describe the corresponding algebra of Weyl-symmetrized functions in coordinate and momentum operators satisfying nonlinear commutation relations. The multiplication in this algebra generates an associative product of functions on the phase space. This product is given by an integral kernel whose phase is the symplectic area of a groupoid-consistent membrane. A symplectic phase space connection with non-trivial curvature is extracted from the magnetic reflections associated with the Stratonovich quantizer. Zero and constant curvature cases are considered as examples. The quantization with both static and time dependent electromagnetic fields is obtained. The expansion of the product by the deformation parameter, written in the covariant form, is compared with the known deformation quantization formulas.

Geometric phases for corotating elliptical vortex patches

We describe a geometric phase that arises when two elliptical vortex patches corotate. Using the Hamiltonian moment model of Melander, Zabusky, and Styczek [J. Fluid Mech. 167, 95–115 (1986)] we consider two corotating uniform elliptical patches evolving according to the second order truncated equations of the model. The phase is computed in the adiabatic setting of a slowly varying Hamiltonian as in the work of Hannay [J. Phys. A 18, 221–230 (1985)] and Berry [Proc. R. Soc. London, Ser. A 392, 45–57 (1984)]. We also discuss the geometry of the symplectic phase space of the model in the context of nonadiabatic phases. The adiabatic phase appears in the orientation angle of each patch—it is similiar in form and is calculated using a multiscale perturbation procedure as in the point vortex configuration of Newton [Physica D 79, 416–423 (1994)] and Shashikanth and Newton [J. Nonlinear Sci. 8, 183–214 (1998)], however, an extra factor due to the internal stucture of the patch is present. The final result depends on the initial orientation of the patches unlike the phases in the works of Hannay and Berry [J. Phys. A 18, 221–230 (1985)]; [Proc. R. Soc. London, Ser. A 392, 45–57 (1984)]. We then show that the adiabatic phase can be interpreted as the holonomy of a connection on the trivial principal fiber bundle π:T2×S1→S1, where T2 is identified with the product of the momentum level sets of two Kirchhoff vortex patches and S1 is diffeomorphic to the momentum level set of two point vortex motion. This two point vortex motion is the motion that the patch centroids approach in the adiabatic limit.

On squeezing and flow of energy for nonlinear wave equations

We study the nonlinear wave equationu−δ2Δu+f(u)=0 undern-dimensional periodic boundary conditions (n=1,2,3) in a Sobolev phase-space\(H^3 = H^3 \times H^{3 - 1} (\mathbb{T}^n ) = \left\{ {(u,\dot u)(x)} \right\}\). In [K1] we interpreted the “energy transition to higher frequencies” problem for this (and similar) equations as a squeezing: time-t flow maps of the equation with larget “squeeze”r-balls inH3 to narrow cylinders formed by vector-functions such that the norms of their first Fourier coefficients are less then some small γ. We proved in [K1] a version of Gromov's (non)squeezing theorem: the phenomenon stated above is impossible for γ<r ifH3 is chosen to be the symplectic phase space of the equation,H3=H1/2. In this paper we show that in smooth phase spacesH3,s≥5, the squeezing is typical if the dispersion δ is small. We use this result and some related statements to obtain a (rather rough) picture of qualitative behaviour of solutions of theϕ4u−δ2Δu+u3=0.

Quantization and bosonic BRST theory

We show that BRST symmetry has a natural bosonic analogue in symplectic geometry. In fact, bosonic BRST theory arises as a purely symplectic construction, which can naturally be viewed as a specific instance of symplectic induction. In this context, both the BRST charge and the total ghost number appear as the “components” of a momentum map on an extended symplectic phase space. Our approach to bosonic BRST theory is motivated by certain problems which arise in the quantization of constrained classical systems. We show that the usual Dirac quantization prescription is incorrect when the system has nonunimodular symmetries and demonstrate how bosonic BRST theory may be used to rectify this. As a byproduct we also prove, under certain circumstances, that both the processes of induction and reduction commute with quantization.

Quantum ergodicity of a coherence-preserving SU(2) Hamiltonian system with quasiperiodic kicking.

In this paper we study the time evolution of a quasiperiodically kicked spin system whose Hamiltonian is linear in the SU(2) generators. Since this Hamiltonian preserves SU(2) coherent states under time evolution, there is a close correspondence between the quantum evolution and the classical evolution of the system on the Bloch sphere. Such a system has previously been studied by Milonni, Ackerhalt, and Goggin [Phys. Rev. A 35, 1714 (1987)] and, with two incommensurate driving frequencies, the quantum evolution was characterized by (a) decay of the autocorrelation function of the state vector, (b) broadband power spectrum of observables, (c) ergodicity on the Bloch sphere. We expand upon their work to study the corresponding behavior of the motion on a symplectic phase space and the decay of the autocorrelation function of the state vector. When the forcing strength is such that the motion is localized in phase space, the autocorrelation function shows revivals. When the motion is ergodic the autocorrelation function rapidly decays without revivals. The classical motion however is not chaotic, there is no sensitive dependence on initial conditions. For three incommensurate frequencies, the motion is more delocalized than for two frequencies for a fixed forcing strength.

Extended coupled-cluster method. I. Generalized coherent bosonization as a mapping of quantum theory into classical Hamiltonian mechanics.

The quantum-mechanical many-body problem is studied using the extended coupled-cluster method (ECCM) as a convenient parametrization of the Hilbert space. A systematic development of the formalism is given, and the quantum-mechanical problem is cast into the form of a classical Hamiltonian field theory in a complex symplectic phase space. The equations of motion of the basic ECCM amplitudes are derived both from a dynamical action principle using the ECCM average-value functional, and directly from the Schr\"odinger equation using the ECCM double similarity transformation. Rules are given for the construction of the Hamiltonian and other observables as well as their products. In particular, commutators are shown to be mapped into generalized classical Poisson brackets. The description is interpreted as an exact bosonization of the quantum theory in which the concept of bosonization is carried to the logical extreme, namely, the resulting generalized coherent bosons are identifiable with classical fields. The quantum-mechanical states of the system are points in the ECCM phase space, and their time evolution, or trajectories, are controlled by a classical Hamiltonian. The bosonization has a perturbation-theoretical basis in terms of maximally linked generalized tree diagrams. The increased degree of locality of the basic amplitudes allows applications to topological excitations and cases with spontaneous symmetry breaking.