Black holes without boundaries

We discuss some of the drawbacks of using event horizons to define black holes and suggest ways in which black holes can be described without event horizons, using trapping horizons. We show that these trapping horizons give rise to thermodynamic behavior and possibly Hawking radiation too. This raises the issue of whether the event horizon or the trapping horizon should be seen as the true boundary of a black hole. This difference is important if we believe that quantum gravity will resolve the central singularity of the black hole and clarifies several of the issues associated with black hole thermodynamics and information loss.Comment: 8 pages. Invited essay for special edition of the International Journal of Modern Physics

High purity bright single photon source

Using cavity-enhanced non-degenerate parametric downconversion, we have built a frequency tunable source of heralded single photons with a narrow bandwidth of 8 MHz, making it compatible with atomic quantum memories. The photon state is 70% pure single photon as characterized by a tomographic measurement and reconstruction of the quantum state, revealing a clearly negative Wigner function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz bandwidth, making it one of the brightest single photon sources available. We also investigate the correlation function of the down-converted fields using a combination of two very distinct detection methods; photon counting and homodyne measurement.Comment: 9 pages, 4 figures; minor changes, added referenc

Why Nature has made a choice of one time and three space coordinates?

We propose a possible answer to one of the most exciting open questions in physics and cosmology, that is the question why we seem to experience four- dimensional space-time with three ordinary and one time dimensions. We have known for more than 70 years that (elementary) particles have spin degrees of freedom, we also know that besides spin they also have charge degrees of freedom, both degrees of freedom in addition to the position and momentum degrees of freedom. We may call these ''internal degrees of freedom '' the ''internal space'' and we can think of all the different particles, like quarks and leptons, as being different internal states of the same particle. The question then naturally arises: Is the choice of the Minkowski metric and the four-dimensional space-time influenced by the ''internal space''? Making assumptions (such as particles being in first approximation massless) about the equations of motion, we argue for restrictions on the number of space and time dimensions. (Actually the Standard model predicts and experiments confirm that elementary particles are massless until interactions switch on masses.) Accepting our explanation of the space-time signature and the number of dimensions would be a point supporting (further) the importance of the ''internal space''.Comment: 13 pages, LaTe

Time gating of heralded single photons for atomic memories

We demonstrate a method for time gating the standard heralded continuous- wave (cw) spontaneous parametric down-converted (SPDC) single photon source by using pulsed pumping of the optical parametric oscillator (OPO) below threshold. The narrow bandwidth, high purity, high spectral brightness and the pseudo-deterministic character make the source highly suitable for light-atom interfaces with atomic memories.Comment: Accepted for publication in Optics Letter

Fermionization, Number of Families

We investigate bosonization/fermionization for free massless fermions being equivalent to free massless bosons with the purpose of checking and correcting the old rule by Aratyn and one of us (H.B.F.N.) for the number of boson species relative to the number of fermion species which is required to have bosonization possible. An important application of such a counting of degrees of freedom relation would be to invoke restrictions on the number of families that could be possible under the assumption, that all the fermions in nature are the result of fermionizing a system of boson species. Since a theory of fundamental fermions can be accused for not being properly local because of having anticommutativity at space like distances rather than commutation as is more physically reasonable to require, it is in fact called for to have all fermions arising from fermionization of bosons. To make a realistic scenario with the fermions all coming from fermionizing some bosons we should still have at least some not fermionized bosons and we are driven towards that being a gravitational field, that is not fermionized. Essentially we reach the spin-charge-families theory by one of us (N.S.M.B.) with the detail that the number of fermion components and therefore of families get determined from what possibilities for fermionization will finally turn out to exist. The spin-charge-family theory has long been plagued by predicting 4 families rather than the phenomenologically more favoured 3. Unfortunately we do not yet understand well enough the unphysical negative norm square components in the system of bosons that can fermionize in higher dimensions because we have no working high dimensional case of fermionization. But suspecting they involve gauge fields with complicated unphysical state systems the corrections from such states could putatively improve the family number prediction.Comment: 30 pages, H.B. Nielsen presented the talk at $20^{\rm{th}}$ Workshop "What Comes Beyond the Standard Models", Bled, 09-17 of July, 201

Multimode analysis of the light emitted from a pulsed optical parametric oscillator

We present a multimode treatment of the optical parametric oscillator, which is valid for both pulsed and continuous-wave pump fields. The two-time correlation functions of the output field are derived, and we apply the theory to analyze a scheme for heralded production of non-classical field states that may be subsequently stored in an atomic quantum memory.Comment: 11 pages, 6 figure