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H. A. Kastrup

Publications and source records attributed to H. A. Kastrup.

At least 19 recordsLinked to original sources

Can the zero-point energy of the quantized harmonic oscillator be lower? Possible implications for the physics of "dark energy" and "dark matter"

Replacing the canonical pair q and p of the harmonic oscillator (HO) by the locally and symplectically equivalent pair angle phi and action variable I implies a qualitative change of the global topological structure of the associated phase spaces: the pair (q,p) is an element of a topologically trivial plane R^2 whereas the pair (phi,I>0) is an element of a topologically non-trivial, infinitely connected, punctured plane R^2-{0}, which has the group SO(1,2) as its "canonical" group. Due to its infinitely many covering groups the resulting ("symplectic") spectrum of the associated quantum Hamiltonian is given by {hbar omega (n+b), n =0,1,...; b in (0,1]}, in contrast to the "orthodox" spectrum {hbar omega (n+1/2)}. The potentially most important implications concern the vibrations of diatomic molecules in the infrared, e.g. those of molecular hydrogen H_2. Those symplectic spectra of the HO may provide a simultaneous key to two outstanding astrophysical puzzles, namely the nature of dark (vacuum) energy and that of dark matter: To the former because the zero-point energy b hbar omega of free electromagnetic wave oscillator modes can be extremely small > 0 (b ca. exp(-35) for the measured dark energy density). And a key to the dark matter problem because the quantum zero-point energies of the Born-Oppenheimer potentials in which the two nuclei of H_2 or the nuclei of other primordial diatomic molecules vibrate can be lower, too, and, therefore, may lead to spectrally detuned "dark" H_2 molecules during the "Dark Ages" of the universe and forming WIMPs in the hypothesized sense. All results appear to be in surprisingly good agreement with the LambdaCDM model of the universe. Besides laboratory experiments the search for 21-cm radio signals from the Dark Ages of the universe and other astrophysical observations can help to explore those hypothetical implications.

physics.gen-ph

Wigner functions for the pair angle and orbital angular momentum: Possible applications in quantum information

The framework of Wigner functions for the canonical pair angle and orbital angular momentum, derived and analyzed in 2 recent papers [H. A. Kastrup, Phys.Rev. A 94, 062113(2016) and Phys.Rev. A 95, 052111(2017)] is applied to elementary concepts of quantum information like qubits and 2-qubits, e.g., entangled EPR/Bell states etc. Properties of the associated Wigner functions of such superposed states (pure and mixed) are discussed and illustrated. The Wigner functions of ERP/Bell states are distinguished by their topologically "twisted" domain on the configuration subspace S^1xS^1, a torus, of the total phase space. Like the applications of Wigner functions in quantum optics the results presented in the present paper may be useful for the description and analysis of quantum information experiments with orbital angular momenta of light beams or electron beams, respectively.

quant-ph

Wigner functions for angle and orbital angular momentum: Operators and dynamics

Recently a paper on the construction of consistent Wigner functions for cylindrical phase spaces S^1 x R, i.e. for the canonical pair angle and angular momentum, was presented (arXiv:1601.02520), main properties of those functions derived, discussed and their usefulness illustrated by examples. The present paper is a continuation which compares properties of the new Wigner functions for cylindrical phase spaces with those of the well-known Wigner functions on planar ones in more detail. Furthermore, the mutual (Weyl) correspondence between Hilbert space operators and their phase space functions is discussed. The star product formalism is shown to be completely implementable. In addition basic dynamical laws for the new Wigner and Moyal functions are derived as generalized quantum Liouville and energy equations. They are very similar to those of the planar case, but also show characteristic differences.

quant-ph

Wigner Functions for the Pair Angle and Orbital Angular Momentum

The problem of constructing physically and mathematically well-defined Wigner functions for the canonical pair angle and angular momentum is solved. While a key element for the construction of Wigner functions for the planar phase space (q,p) in R^2 is the Heisenberg-Weyl group, the corresponding group for the cylindrical phase space (theta,p) in S^1 x R is the Euclidean group E(2) of the plane and its unitary representations. Here the angle theta is replaced by the pair (cos theta, sin theta) which corresponds uniquely to the points on the unit circle. The main structural properties of the Wigner functions for the planar and the cylindrical phase spaces are strikingly similar. A crucial role plays the sinc function which provides the interpolation for the discontinuous quantized angular momenta in terms of the continuous classical ones, in accordance with the famous Whittaker cardinal function, well-known from interpolation and sampling theories. The quantum mechanical marginal distributions for angle (continuous) and angular momentum (discontinuous) are as usual uniquely obtained by appropriate integrations of the (theta,p) Wigner function. Among the examples discussed is an elementary system of simple "cat" states.

quant-ph

On the Advancements of Conformal Transformations and their Associated Symmetries in Geometry and Theoretical Physics

The historical developments of conformal transformations and symmetries are sketched: Their origin from stereographic projections of the globe, their blossoming in two dimensions within the field of analytic complex functions, the generic role of transformations by reciprocal radii in dimensions higher than two and their linearization in terms of polyspherical coordinates by Darboux, Weyl's attempt to extend General Relativity, the slow rise of finite dimensional conformal transformations in classical field theories and the problem of their interpretation, then since about 1970 the rapid spread of their acceptance for asymptotic and structural problems in quantum field theories and beyond, up to the current AdS/CFT conjecture. The occasion for the present article: hundred years ago Bateman and Cunningham discovered the form invariance of Maxwell's equations for electromagnetism with respect to conformal space-time transformations.

physics.hist-ph

A New Look at the Quantum Mechanics of the Harmonic Oscillator

Classically the Harmonic Oscillator (HO) is the generic example for the use of angle and action variables phi in R mod 2 pi and I > 0. But the symplectic transformation (ϕ,I) to (q,p) is singular for (q,p) = (0,0). Globally {(q,p)} has the structure of the plane R^2, but {(phi,I)} that of the punctured plane R^2 -(0,0). This implies qualitative differences for the QM of the two phase spaces: The quantizing group for the plane R^2 consists of the (centrally extended) translations generated by {q,p,1}, but the corresponding group for {(phi,I)} is SO(1,2) = Sp(2,R)/Z_2, (Sp(2,R): symplectic group of the plane), with Lie algebra basis {h_0 = I, h_1 = I cos phi, h_2 = - I sin phi}. In the QM for the (phi,I)-model the three h_j correspond to self-adjoint generators K_j, j=0,1,2, of irreducible unitary representations (positive discrete series) for SO(1,2) or one of its infinitely many covering groups, the Bargmann index k > 0 of which determines the ground state energy E (k, n=0) = hbar omega k of the (phi,I)-Hamiltonian H(K). For an m-fold covering the lowest possible value is k=1/m, which can be made arbitrarily small! The operators Q and P, now expressed as functions of the K_j, keep their usual properties, but the richer structure of the K_j quantum model of the HO is ``erased'' when passing to the simpler Q,P model! The (phi,I)-variant of the HO implies many experimental tests: Mulliken-type experiments for isotopic diatomic molecules, experiments with harmonic traps for atoms, ions and BE-condensates, with the (Landau) levels of charged particles in magnetic fields, with the propagation of light in vacuum, passing through electric or magnetic fields. Finally it leads to a new theoretical estimate for the quantum vacuum energy of fields and its relation to the cosmological constant.

quant-ph

Quantization of the Optical Phase Space S^2 = {phi mod 2pi, I > 0} in Terms of the Group SO(1,2)

The problem of quantizing the canonical pair angle and action variables phi and I is almost as old as quantum mechanics itself and since decades a strongly debated but still unresolved issue in quantum optics. The present paper proposes a new approach to the problem, namely quantization in terms of the group SO(1,2): The crucial point is that the phase space S^2 = {phi mod 2pi, I>0} has the global structure S^1 x R^+ (a simple cone) and cannot be quantized in the conventional manner. As the group SO(1,2) acts appropriately on that space its unitary representations of the positive discrete series provide the correct quantum theoretical framework. The space S^2 has the conic structure of an orbifold R^2/Z_2. That structure is closely related to the center Z_2 of the symplectic group Sp(2,R). The basic variables on S^2 are the functions h_0 = I, h_1 = I cosphi and h_2 = -I sinphi, the Poisson brackets of which obey the Lie algebra so(1,2). In the quantum theory they are represented by self-adjoint generators K_0, K_1 and K_2 of a unitary representation. A crucial prediction is that the classical Pythagorean relation h_1^2+h_2^2 = h_0^2 may be violated in the quantum theory. For each representation one can define 3 different types of coherent states the complex phases of which can be "measured" by means of K_1 and K_2 alone without introducing any new phase operators! The SO(1,2) structure of optical squeezing and interference properties as well as that of the harmonic oscillator are analyzed in detail. The new coherent states can be used for the introduction of (Husimi type) Q and (Sudarshan-Glauber type) P representations of the density operator. The 3 operators K_0, K_1 and K_2 are fundamental in the sense that one can construct (composite) position and momentum operators out of them!

quant-ph

Quantization of the canonically conjugate pair angle and orbital angular momentum

The question how to quantize a classical system where an angle phi is one of the basic canonical variables has been controversial since the early days of quantum mechanics. The problem is that the angle is a multivalued or discontinuous variable on the corresponding phase space. The remedy is to replace phi by the smooth periodic functions cos phi and sin phi. In the case of the canonical pair (phi,l),l: orbital angular momentum (OAM), the phase space S_(phi,l) ={phi in R mod 2pi, l in R} has the global structure S^1 x R of a cylinder on which the Poisson brackets of the 3 functions cos phi, sin phi and l obey the Lie algebra of the euclidean group E(2) in the plane. This property provides the basis for the quantization of the system in terms of irreducible unitary representations of the group E(2) or of its covering groups. A crucial point is that - due to the fact that the subgroup SO(2) = S^1 is multiply connected - these representations allow for fractional OAM l = n + c, c in [0,1). Such c not 0 have already been observed in cases like the Aharonov-Bohm and the fractional quantum Hall effects and they correspond to the quasi-momenta of Bloch waves in ideal crystals. The proposal of the present paper is to look for fractional OAM in connection with the quantum optics of Laguerre-Gaussian laser modes in external magnetic fields. The quantum theory of the phase space S_(phi,l) in terms of unitary representations of E(2) allows for two types of "coherent" states the properties of which are discussed in detail: Non-holomorphic minimal uncertainty states and holomorphic ones associated with Bargmann-Segal Hilbert spaces.

quant-ph

How to Quantize Phases and Moduli!

A typical classical interference pattern of two waves with intensities I_1, I_2 and relative phase phi = phi_2-phi_1 may be characterized by the 3 observables p = sqrt{I_1 I_2}, p cosϕand -p sinϕ. They are, e.g. the starting point for the semi-classical operational approach by Noh, Fougeres and Mandel (NFM) to the old and notorious phase problem in quantum optics. Following a recent group theoretical quantization of the symplectic space S = {(phi in R mod 2pi, p > 0)} in terms of irreducible unitary representations of the group SO(1,2) the present paper applies those results to that controversial problem of quantizing moduli and phases of complex numbers: The Poisson brackets of the classical observables p cosϕ, -p sinϕand p > 0 form the Lie algebra of the group SO(1,2). The corresponding self-adjoint generators K_1, K_2 and K_3 of that group may be obtained from its irreducible unitary representations. For the positive discrete series the modulus operator K_3 has the spectrum {k+n, n = 0, 1,2,...; k > 0}. Self-adjoint operators for cos phi and sin phi can be defined as ((1/K_3)K_1 + K_1/K_3)/2 and -((1/K_3)K_2 + K_2/K_3)/2 which have the theoretically desired properties for k > or = 0.5. The approach advocated here solves, e.g. the modulus-phase quantization problem for the harmonic oscillator and appears to provide a full quantum theoretical basis for the NFM-formalism.

quant-ph

Symmetric States in Quantum Geometry

Symmetric states are defined in the kinematical sector of loop quantum gravity and applied to spherical symmetry and homogeneity. Consequences for the physics of black holes and cosmology are discussed.

gr-qc

Group Theoretical Quantization of Phase and Modulus Related to Interferences

Following a recent group theoretical quantization of the symplectic space S={(phi in R mod 2pi, p>0)} in terms of irreducible unitary representations of the group SO(1,2) the present paper proposes an application of those results to the old problem of quantizing modulus and phase in interference phenomena: The self-adjoint Lie algebra generators K_1, K_2 and K_3 of that group correspond to the classical observables p cos(phi), -p sin(phi) and p > 0 the Poisson brackets of which obey that Lie algebra, too. For the irreducible unitary representations of the positive series the modulus operator K_3 has the positive discrete spectrum {n+k, n=0,1,2,...; k > 0}. Self-adjoint operators for cos(phi) and sin(phi) can then be defined as (K_3^{-1}K_1 + K_1 K_3^{-1})/2 and - (K_3^{-1} K_2 + K_2 K_3^{-1})/2 which have the theoretically desired properties for k >0.32. Some matrix elements with respect to number eigenstates and with respect to coherent states are calculated. One conclusion is that group theoretical quantization may be tested by quantum optical experiments.

quant-ph

Schwarzschild Black Hole Quantum Statistics from Z(2) Orientation Degrees of Freedom and its Relations to Ising Droplet Nucleation

Generalizing previous quantum gravity results for Schwarzschild black holes from 4 to D > 3 space-time dimensions yields an energy spectrum E_n = alpha n^{(D-3)/(D-2)} E_P, n=1,2,..., alpha = O(1), where E_P is the Planck energy in that space-time. This spectrum means that the quantized area A_{D-2}(n) of the D-2 dimensional horizon has universally the form A_{D-2} = n a_{D-2}, where a_{D-2} is essentially the (D-2)th power of the D-dimensional Planck length. Assuming that the basic area quantum has a Z(2)-degeneracy according to its two possible orientation degrees of freedom implies a degeneracy d_n = 2^n for the n-th level. The energy spectrum with such a degeneracy leads to a quantum canonical partition function which is the same as the classical grand canonical partition function of a primitive Ising droplet nucleation model for 1st-order phase transitions in D-2 spatial dimensions. The analogy to this model suggests that E_n represents the surface energy of a "droplet" of n horizon quanta. Exploiting the well-known properties of the so-called critical droplets of that model immediately leads to the Hawking temperature and the Bekenstein-Hawking entropy of Schwarzschild black holes. The values of temperature and entropy appear closely related to the imaginary part of the partition function which describes metastable states

gr-qc

Group Theoretical Quantization of a Phase Space S^1 x R^+ and the Mass Spectrum of Schwarzschild Black Holes in D Space-Time Dimensions

The symplectic reduction of pure spherically symmetric (Schwarzschild) classical gravity in D space-time dimensions yields a 2-dimensional phase space of observables consisting of the Mass M (>0) and a canonically conjugate (Killing) time variable T. Imposing (mass-dependent) periodic boundary conditions in time on the associated quantum mechanical plane waves which represent the Schwarzschild system in the period just before or during the formation of a black hole, yields an energy spectrum of the hole which realizes the old Bekenstein postulate that the quanta of the horizon A_{D-2} are multiples of a basic area quantum. In the present paper it is shown that the phase space of such a Schwarzschild black hole in D space-time dimensions is symplectomorphic to a symplectic manifold S={(phi in R mod 2 pi, p = A_{D-2} >0)} with the symplectic form d phi wedge d p. As the action of the group SO_+(1,2) on that manifold is transitive, effective and Hamiltonian, it can be used for a group theoretical quantization of the system. The area operator p for the horizon corresponds to the generator of the compact subgroup SO(2) and becomes quantized accordingly: The positive discrete series of the irreducible unitary representations of SO_+(1,2) yields an (horizon) area spectrum proportional k+n, where k =1,2,... characterizes the representation and n = 0,1,2,... the number of area quanta. If one employs the unitary representations of the universal covering group of SO_+(1,2) the number k can take any fixed positive real value (theta-parameter). The unitary representations of the positive discrete series provide concrete Hilbert spaces for quantum Schwarzschild black holes.

gr-qc

Quantum Symmetry Reduction for Diffeomorphism Invariant Theories of Connections

Given a symmetry group acting on a principal fibre bundle, symmetric states of the quantum theory of a diffeomorphism invariant theory of connections on this fibre bundle are defined. These symmetric states, equipped with a scalar product derived from the Ashtekar-Lewandowski measure for loop quantum gravity, form a Hilbert space of their own. Restriction to this Hilbert space yields a quantum symmetry reduction procedure in the framework of spin network states the structure of which is analyzed in detail. Three illustrating examples are discussed: Reduction of 3+1 to 2+1 dimensional quantum gravity, spherically symmetric electromagnetism and spherically symmetric gravity.

hep-th

Mass spectrum and elastic scattering in the massive SU(2)_f Schwinger model on the lattice

We calculate numerically scattering phases for elastic meson-meson scattering processes in the strongly coupled massive Schwinger-model with an SU(2) flavour symmetry. These calculations are based on Luescher's method in which finite size effects in two-particle energies are exploited. The results from Monte-Carlo simulations with staggered fermions for the lightest meson ("pion") are in good agreement with the analytical strong-coupling prediction. Furthermore, the mass spectrum of low-lying mesonic states is investigated numerically. We find a surprisingly rich spectrum in the mass region [m_π,4 m_π].

hep-lat

Schwarzschild Black Hole Quantum Statistics, Droplet Nucleation and DLCQ Matrix Theory

Generalizing previous quantum gravity results for Schwarzschild black holes from 4 to D>4 spacetime dimensions yields an energy spectrum E_n = n^{1-1/(D-2)} sigma E_P, n=1,2,..., sigma = O(1). Assuming the degeneracies of these levels to be given by g^n, g>1, leads to a partition function which is the same as that of the primitive droplet nucleation model for 1st-order phase transitions in D-2 spatial dimensions. Exploiting the well-known properties of the so-called critical droplets of this model immediately leads to the Hawking temperature and the Bekenstein-Hawking entropy of Schwarzschild black holes. Thus, the "holographic principle" of 't Hooft and Susskind is naturally realised. The values of temperature and entropy appear closely related to the imaginary part of the partition function which describes metastable states. Finally some striking conceptual similarities ("correspondence point" etc.) between the droplet nucleation picture and the very recent approach to the quantum statistics of Schwarzschild black holes in the framework of the DLCQ Matrix theory are pointed out.

hep-th

Exact Partition Functions for the Primitive Droplet Nucleation Model in 2 and 3 Dimensions

The grand canonical partition functions for primitive droplet nucleation models with an excess energy epsilon_n = - mu n + sigma n^{1-eta}, eta = 1/d, for droplets of n constituents in d dimensions are calculated exacly in closed form in the cases d=2 and 3 for all (complex) mu by exploiting the fact that the partition functions obey simple PDE.

cond-mat.stat-mech

Canonical Quantum Statistics of Schwarzschild Black Holes and Ising Droplet Nucleation

Recently is was shown that the imaginary part of the canonical partition function of Schwarzschild black holes with an energy spectrum E_n = σ\sqrt{n} E_P, n= 1,2, ..., has properties which - naively interpreted - leads to the expected unusual thermodynamical properties of such black holes (Hawking temperature, Bekenstein-Hawking entropy etc). The present paper interprets the same imaginary part in the framework of droplet nucleation theory in which the rate of transition from a metastable state to a stable one is proportional to the imaginary part of the canonical partition function. The conclusions concerning the emerging thermodynamics of black holes are essentially the same as before. The partition function for black holes with the above spectrum was calculated exactly recently. It is the same as that of the primitive Ising droplet model for nucleation in 1st-order phase transitions in 2 dimensions. Thus one might learn about the quantum statistics of black holes by studying that Ising model, the exact complex free energy of which is presented here for negative magnetic fields, too.

gr-qc