arXiv subjects

Jorma Louko

Publications and source records attributed to Jorma Louko.

At least 55 records · Page 3Linked to original sources

arXiv2018

Smooth and sharp creation of a spherical shell for a $(3+1)$-dimensional quantum field

We study the creation of a spherical, finite radius source for a quantized massless scalar field in 3+1 dimensions. The goal is to model the breakdown of correlations that has been proposed to occur at the horizon of an evaporating black hole. We do this by introducing at fixed radius $r=a$ a one parameter family of self-adjoint extensions of the three dimensional Laplacian operator that interpolate between the condition that the values and the derivatives on the two sides of $r=a$ coincide for $t\le0$ (no wall) and the two-sided Dirichlet boundary condition for $t \ge 1/λ$ (fully-developed wall). Creation of the shell produces null, spherical pulses of energy on either side of the shell, one ingoing and the other outgoing. The renormalized energy density $\langle T_{00}\rangle$ diverges to positive infinity in the outgoing energy pulse, just outside the light cone of the fully-formed wall at $t=1/λ$. Unlike in the 3+1 point source creation, there is no persistent memory cloud of energy. As in the creation of a 1+1 dimensional wall, the response of an Unruh-DeWitt detector in the post-shell region is independent of the time scale for shell formation and is finite. The latter property casts doubt on the efficacy of this mechanism for firewall creation.

gr-qc↗

arXiv2017

Gravitational memory for uniformly accelerated observers

Recently, Hawking, Perry and Strominger described a physical process that implants supertranslational hair on a Schwarzschild black hole by an infalling matter shock wave without spherical symmetry. Using the BMS-type symmetries of the Rindler horizon, we present an analogous process that implants supertranslational hair on a Rindler horizon by a matter shock wave without planar symmetry, and we investigate the corresponding memory effect on the Rindler family of uniformly linearly accelerated observers. We assume each observer to remain linearly uniformly accelerated through the wave, in the sense of the curved spacetime generalisation of the Letaw-Frenet equations. Starting with a family of observers who follow the orbits of a single boost Killing vector before the wave, we find that after the wave has passed, each observer still follows the orbit of a boost Killing vector but this boost differs from trajectory to trajectory, and the trajectory-dependence carries a memory of the planar inhomogeneity of the wave. We anticipate this classical memory phenomenon to have a counterpart in Rindler space quantum field theory.

hep-th↗

arXiv2017

Quantum communications and quantum metrology in the spacetime of a rotating planet

We study how quantum systems that propagate in the spacetime of a rotating planet are affected by the curved background. Spacetime curvature affects wavepackets of photons propagating from Earth to a satellite, and the changes in the wavepacket encode the parameters of the spacetime. This allows us to evaluate quantitatively how quantum communications are affected by the curved spacetime background of the Earth and to achieve precise measurements of Earth's Schwarzschild radius and equatorial angular velocity. We then provide a comparison with the state of the art in parameter estimation obtained through classical means. Satellite to satellite communications and future directions are also discussed.

quant-ph↗

arXiv2017

Degenerate detectors are unable to harvest spacelike entanglement

We show, under a very general set of assumptions, that pairs of identical particle detectors in spacelike separation, such as atomic probes, can only harvest entanglement from the vacuum state of a quantum field when they have a non-zero energy gap. Furthermore, we show that degenerate probes are strongly challenged to become entangled through their interaction through scalar and electromagnetic fields even in full light-contact. We relate these results to previous literature on remote entanglement generation and entanglement harvesting, giving insight into the energy gap's protective role against local noise, which prevents the detectors from getting entangled through the interaction with the field.

quant-ph↗

arXiv2017

Smooth and sharp creation of a pointlike source for a $(3+1)$-dimensional quantum field

We analyse the smooth and sharp creation of a pointlike source for a quantised massless scalar field in $(3+1)$-dimensional Minkowski spacetime, as a model for the breakdown of correlations that has been proposed to occur at the horizon of an evaporating black hole. The creation is implemented by a time-dependent self-adjointness parameter at the excised spatial origin. In a smooth creation, the renormalised energy density $\langle T_{00} \rangle$ is well defined away from the source, but it is unbounded both above and below: the outgoing pulse contains an infinite negative energy, while a cloud of infinite positive energy lingers near the fully-formed source. In the sharp creation limit, $\langle T_{00} \rangle$ diverges everywhere in the timelike future of the creation event, and so does the response of an Unruh-DeWitt detector that operates in the timelike future of the creation event. The source creation is significantly more singular than the corresponding process in $1+1$ dimensions, analysed previously, and it may be sufficiently singular to break quantum correlations as proposed in a black hole spacetime.

hep-th↗

arXiv2017

Smooth and sharp creation of a Dirichlet wall in 1+1 quantum field theory: how singular is the sharp creation limit?

We present and utilize a simple formalism for the smooth creation of boundary conditions within relativistic quantum field theory. We consider a massless scalar field in $(1+1)$-dimensional flat spacetime and imagine smoothly transitioning from there being no boundary condition to there being a two-sided Dirichlet mirror. The act of doing this, expectantly, generates a flux of real quanta that emanates from the mirror as it is being created. We show that the local stress-energy tensor of the flux is finite only if an infrared cutoff is introduced, no matter how slowly the mirror is created, in agreement with the perturbative results of Obadia and Parentani. In the limit of instantaneous mirror creation the total energy injected into the field becomes ultraviolet divergent, but the response of an Unruh-DeWitt particle detector passing through the infinite burst of energy nevertheless remains finite. Implications for vacuum entanglement extraction and for black hole firewalls are discussed.

hep-th↗

arXiv2016

Unruh-DeWitt detector's response to fermions in flat spacetimes

We examine an Unruh-DeWitt particle detector that is coupled linearly to the scalar density of a massless Dirac field in Minkowski spacetimes of dimension $d\ge2$ and on the static Minkowski cylinder in spacetime dimension two, allowing the detector's motion to remain arbitrary and working to leading order in perturbation theory. In $d$-dimensional Minkowski, with the field in the usual Fock vacuum, we show that the detector's response is identical to that of a detector coupled linearly to a massless scalar field in $2d$-dimensional Minkowski. In the special case of uniform linear acceleration, the detector's response hence exhibits the Unruh effect with a Planckian factor in both even and odd dimensions, in contrast to the Rindler power spectrum of the Dirac field, which has a Planckian factor for odd $d$ but a Fermi-Dirac factor for even~$d$. On the two-dimensional cylinder, we set the oscillator modes in the usual Fock vacuum but allow an arbitrary state for the zero mode of the periodic spinor. We show that the detector's response distinguishes the periodic and antiperiodic spin structures, and the zero mode of the periodic spinor contributes to the response by a state-dependent but well defined amount. Explicit analytic and numerical results on the cylinder are obtained for inertial and uniformly accelerated trajectories, recovering the $d=2$ Minkowski results in the limit of large circumference. The detector's response has no infrared ambiguity for $d=2$, neither in Minkowski nor on the cylinder.

gr-qc↗

arXiv2016

Waiting for Unruh

How long does a uniformly accelerated observer need to interact with a quantum field in order to record thermality in the Unruh temperature? We address this question for a pointlike Unruh-DeWitt detector, coupled linearly to a real Klein-Gordon field of mass $m\ge0$ and treated within first order perturbation theory, in the limit of large detector energy gap $E_{\text{gap}}$. We first show that when the interaction duration $ΔT$ is fixed, thermality in the sense of detailed balance cannot hold as $E_{\text{gap}}\to\infty$, and this property generalises from the Unruh effect to any Kubo-Martin-Schwinger state satisfying certain technical conditions. We then specialise to a massless field in four spacetime dimensions and show that detailed balance does hold when $ΔT$ grows as a power-law in $E_{\text{gap}}$ as $E_{\text{gap}}\to\infty$, provided the switch-on and switch-off intervals are stretched proportionally to $ΔT$ and the switching function has sufficiently strong Fourier decay. By contrast, if $ΔT$ grows by stretching a plateau in which the interaction remains at constant strength but keeping the duration of the switch-on and switch-off intervals fixed, detailed balance at $E_{\text{gap}}\to\infty$ requires $ΔT$ to grow faster than any polynomial in $E_{\text{gap}}$, under mild technical conditions. These results also hold for a static detector in a Minkowski heat bath. The results limit the utility of the large $E_{\text{gap}}$ regime as a probe of thermality in time-dependent versions of the Hawking and Unruh effects, such as an observer falling into a radiating black hole. They may also have implications on the design of prospective experimental tests of the Unruh effect.

gr-qc↗

arXiv2016

Asymptotically thermal responses for smoothly switched detectors

Thermal phenomena in quantum field theory can be detected with the aid of particle detectors coupled to quantum fields along stationary worldlines, by testing whether the response of such a detector satisfies the detailed balance version of the KMS condition at a constant temperature. This relation holds when the interaction between the field and the detector has infinite time duration. Operationally, however, detectors interact with fields for a finite amount of time, controlled by a switching function of compact support, and the KMS detailed balance condition cannot hold exactly for finite time interactions at arbitrarily large detector energy gap. In this large energy gap regime, we show that, for an adiabatically switched Rindler detector, the Unruh temperature emerges asymptotically after the detector and the field have interacted for a time that is polynomially long in the large energy. We comment on the significance of the adiabaticity assumption in this result.

math-ph↗

arXiv2016

Low energy Lorentz violation from modified dispersion at high energies

Many quantum theories of gravity propose Lorentz violating dispersion relations of the form $ω= |k|\, f(|k|/M)$, with recovery of approximate Lorentz invariance at energy scales much below $M$. We show that a quantum field with this dispersion predicts drastic low energy Lorentz violation in atoms modelled as Unruh-DeWitt detectors, for any $f$ that dips below unity somewhere. As an example, we show that polymer quantization motivated by loop quantum gravity predicts such Lorentz violation below current ion collider rapidities.

gr-qc↗

arXiv2016

Unruh-DeWitt Fermion Detector on a (1+1)-Dimensional Cylindrical Spacetime: Arbitrary Worldlines and Inequivalent Spin Structures

We examine an Unruh-DeWitt particle detector which couples linearly to the scalar density of a massless Dirac field on the static cylindrical quotient of the (1+1)-dimensional Minkowski spacetime, allowing the detector's motion to remain arbitrary and working to leading order in perturbation theory. We show that the detector's response distinguishes the periodic and antiperiodic spin structures, and the zero mode that is present for periodic spinors contributes to the response by a state-dependent but well defined and controllable amount.

gr-qc↗

arXiv2015

Ideal clocks - a convenient fiction

We show that no device built according to the rules of quantum field theory can measure proper time along its path. Highly accelerated quantum clocks experience the Unruh effect, which inevitably influences their time rate. This contradicts the concept of an ideal clock, whose rate should only depend on the instantaneous velocity.

quant-ph↗

arXiv2015

Unruh-DeWitt detector response across a Rindler firewall is finite

We investigate a two-level Unruh-DeWitt detector coupled to a massless scalar field or its proper time derivative in $(1+1)$-dimensional Minkowski spacetime, in a quantum state whose correlation structure across the Rindler horizon mimics the stationary aspects of a firewall that Almheiri et al have argued to ensue in an evaporating black hole spacetime. Within first-order perturbation theory, we show that the detector's response on falling through the horizon is sudden but finite. The difference from the Minkowski vacuum response is proportional to $ω^{-2}\ln(|ω|)$ for the non-derivative detector and to $\ln(|ω|)$ for the derivative-coupling detector, both in the limit of a large energy gap $ω$ and in the limit of adiabatic switching. Adding to the quantum state high Rindler temperature excitations behind the horizon increases the detector's response proportionally to the temperature; this situation has been suggested to model the energetic curtain proposal of Braunstein et al. We speculate that the $(1+1)$-dimensional derivative-coupling detector may be a good model for a non-derivative detector that crosses a firewall in $3+1$ dimensions.

hep-th↗

arXiv2015

(1+1)D Calculation provides evidence that quantum entanglement survives a firewall

We analyze how pre-existing entanglement between two Unruh-DeWitt particle detectors evolves when one of the detectors falls through a Rindler firewall in (1+1)-dimensional Minkowski space. The firewall effect is minor and does not wash out the detector-detector entanglement, in some regimes even preserving the entanglement better than Minkowski vacuum. The absence of cataclysmic events should continue to hold for young black hole firewalls. A firewall's prospective ability to resolve the information paradox must hence hinge on its detailed gravitational structure, presently poorly understood.

quant-ph↗

arXiv2015

Near-Dirichlet quantum dynamics for a $p^3$-corrected particle on an interval

We study a nonrelativistic quantum mechanical particle on an interval of finite length with a Hamiltonian that has a $p^3$ correction term, modelling potential low energy quantum gravity effects. We describe explicitly the $U(3)$ family of the self-adjoint extensions of the Hamiltonian and discuss several subfamilies of interest. As the main result, we find a family of self-adjoint Hamiltonians, indexed by four continuous parameters and one binary parameter, whose spectrum and eigenfunctions are perturbatively close to those of the uncorrected particle with Dirichlet boundary conditions, even though the Dirichlet condition as such is not in the $U(3)$ family. Our boundary conditions do not single out distinguished discrete values for the length of the interval in terms of the underlying quantum gravity scale.

hep-th↗

arXiv2015

Superconducting circuit boundary conditions beyond the Dynamical Casimir Effect

We study analytically the time-dependent boundary conditions of superconducting microwave circuit experiments in the high plasma frequency limit, in which the conditions are Robin-type and relate the value of the field to the spatial derivative of the field. We give an explicit solution to the field evolution for boundary condition modulations that are small in magnitude but may have arbitrary time dependence, in a formalism that applies both to a semiopen waveguide and to a closed waveguide with two independently adjustable boundaries. The correspondence between the microwave Robin boundary conditions and the mechanically-moving Dirichlet boundary conditions of the Dynamical Casimir Effect is shown to break down at high field frequencies, approximately one order of magnitude above the frequencies probed in the 2011 experiment of Wilson et al. Our results bound the parameter regime in which a microwave circuit can be used to model relativistic effects in a mechanically-moving cavity, and they show that beyond this parameter regime moving mirrors produce more particles and generate more entanglement than their non-moving microwave waveguide simulations.

quant-ph↗

arXiv2015

Renormalized vacuum polarization on rotating warped AdS3 black holes

We compute the renormalized vacuum polarization of a massive scalar field in the Hartle-Hawking state on (2+1)-dimensional rotating, spacelike stretched black hole solutions to Topologically Massive Gravity, surrounded by a Dirichlet mirror that makes the state well defined. The Feynman propagator is written as a mode sum on the complex Riemannian section of the spacetime, and a Hadamard renormalization procedure is implemented by matching to a mode sum on the complex Riemannian section of a rotating Minkowski spacetime. No analytic continuation in the angular momentum parameter is invoked. Selected numerical results are given, demonstrating the numerical efficacy of the method. We anticipate that this method can be extended to wider classes of rotating black hole spacetimes, in particular to the Kerr spacetime in four dimensions.

gr-qc↗

arXiv2014

Onset and decay of the 1+1 Hawking-Unruh effect: what the derivative-coupling detector saw

We study an Unruh-DeWitt particle detector that is coupled to the proper time derivative of a real scalar field in 1+1 spacetime dimensions. Working within first-order perturbation theory, we cast the transition probability into a regulator-free form, and we show that the transition rate remains well defined in the limit of sharp switching. The detector is insensitive to the infrared ambiguity when the field becomes massless, and we verify explicitly the regularity of the massless limit for a static detector in Minkowski half-space. We then consider a massless field for two scenarios of interest for the Hawking-Unruh effect: an inertial detector in Minkowski spacetime with an exponentially receding mirror, and an inertial detector in $(1+1)$-dimensional Schwarzschild spacetime, in the Hartle-Hawking-Israel and Unruh vacua. In the mirror spacetime the transition rate traces the onset of an energy flux from the mirror, with the expected Planckian late time asymptotics. In the Schwarzschild spacetime the transition rate of a detector that falls in from infinity gradually loses thermality, diverging near the singularity proportionally to $r^{-3/2}$.

gr-qc↗