上午9:48 | | | quant-ph updates on arXiv.org |

Authors: K. Urbanowski

The Heisenberg and Mandelstam-Tamm time-energy uncertainty relations are analyzed. The conlusion resulting from this analysis is that within the Quantum Mechanics of Schr\”{o}dinger and von Neumann, the status of these relations can not be considered as the same as the status of the position-momentum uncertainty relations, which are rigorous. The conclusion is that the time–energy uncertainty relations can not be considered as universally valid.

上午9:48 | | | gr-qc updates on arXiv.org |

Authors: Manus R. Visser

This dissertation investigates thermodynamic, emergent and holographic aspects of gravity in the context of causal diamonds. We obtain a gravitational first law for causal diamonds in maximally symmetric spacetimes and argue that these diamonds are in thermodynamic equilibrium at negative temperature. Further, gravitational field equations, including higher curvature corrections, are derived from an equilibrium condition on the generalized entropy of small maximally symmetric diamonds. Finally, we assign three holographic microscopic quantities to causal diamonds in spherically symmetric spacetimes, and for non-AdS geometries we interpret them in terms of the long string degrees of freedom of symmetric product conformal field theories.

上午9:48 | | | gr-qc updates on arXiv.org |

Authors: Daniel G. Figueroa, Erwin H. Tanin

The expansion history of the Universe between the end of inflation and the onset of radiation-domination (RD) is currently unknown. If the equation of state during this period is stiffer than that of radiation, $w > 1/3$, the gravitational wave (GW) background from inflation acquires a blue-tilt ${d\log\rho_{\rm GW}\over d\log f} = {2(w-1/3)\over (w+1/3)} > 0$ at frequencies $f \gg f_{\rm RD}$ corresponding to modes re-entering the horizon during the stiff-domination (SD), where $f_{\rm RD}$ is the frequency today of the horizon scale at the SD-to-RD transition. We characterized in detail the transfer function of the GW energy density spectrum, considering both ‘instant’ and smooth modelings of the SD-to-RD transition. The shape of the spectrum is controlled by $w$, $f_{\rm RD}$, and $H_{\rm inf}$ (the Hubble scale of inflation). We determined the parameter space compatible with a detection of this signal by LIGO and LISA, including possible changes in the number of relativistic degrees of freedom, and the presence of a tensor tilt. Consistency with upper bounds on stochastic GW backgrounds, however, rules out a significant fraction of the observable parameter space. We find that this renders the signal unobservable by Advanced LIGO, in all cases. The GW background remains detectable by LISA, though only in a small island of parameter space, corresponding to scenarios with an equation of state in the range $0.46 \lesssim w \lesssim 0.56$ and a high inflationary scale $H_{\rm inf} \gtrsim 10^{13}~{\rm GeV}$, but low reheating temperature $1~{\rm MeV} \lesssim T_{\rm RD} \lesssim 150~{\rm MeV}$ (equivalently, $10^{-11}~{\rm Hz} \lesssim f_{\rm RD} \lesssim 3.6\cdot10^{-9}~{\rm Hz}$). Implications for early Universe scenarios resting upon an SD epoch are briefly discussed.

2019年8月15日 星期四 下午2:03 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0) |

2019年8月15日 星期四 下午2:00 | | | Philsci-Archive: No conditions. Results ordered -Date Deposited. (RSS 2.0) |

2019年8月12日 星期一 上午8:00 | | | Per Delsing | | | Nature Physics – Issue – nature.com science feeds |

Nature Physics, Published online: 12 August 2019; doi:10.1038/s41567-019-0605-6

By coupling a superconducting qubit to surface acoustic waves the ‘giant atom’ regime is realized, where an atom is coupled to a field with wavelength orders of magnitude smaller than the atomic size. This leads to non-Markovian qubit dynamics.

On the E,t uncertainty relations:

Yes, the best derivation I know is that of Schwinger, who assumes an H and H_0. H generates transitions in the levels of H_0, and he estimates the time for moving \Delta E in H_0 to be \Delta E \over \hbar. Certainly not rigorous. In relativistic quantum theory (e.g. my book with Springer 2015) it is established rigorously since, long with x and p. t and E are observables in the covariant theory and have covariant commutation relations. Larry Horwitz