* Astronomy

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RE: Quantum information

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Title: Soft Hair on Black Holes
Author: Stephen W. Hawking, Malcolm J. Perry, Andrew Strominger

It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These laws require black holes to carry a large amount of soft (i.e. zero-energy) supertranslation hair. The presence of a Maxwell field similarly implies soft electric hair. This paper gives an explicit description of soft hair in terms of soft gravitons or photons on the black hole horizon, and shows that complete information about their quantum state is stored on a holographic plate at the future boundary of the horizon. Charge conservation is used to give an infinite number of exact relations between the evaporation products of black holes which have different soft hair but are otherwise identical. It is further argued that soft hair which is spatially localized to much less than a Planck length cannot be excited in a physically realizable process, giving an effective number of soft degrees of freedom proportional to the horizon area in Planck units.

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Information Paradox

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RE: Quantum information

Blobrana · L

'Quantum Cheshire Cat' becomes reality

Scientists have for the first time separated a particle from one of its physical properties - creating a "quantum Cheshire Cat".
The phenomenon is named after the curious feline in Alice in Wonderland, who vanishes leaving only its grin.
Researchers took a beam of neutrons and separated them from their magnetic moment, like passengers and their baggage at airport security.
They describe their feat in Nature Communications.
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Curtains down for the black hole firewall paradox: making gravity safe for Einstein again

Research by scientists at the University of York has revealed new insights into the life and death of black holes.
Their findings dispel the so-called firewall paradox which shocked the physics community when it was announced in 2012 since its predictions about large black holes contradicted Einstein's crowning achievement - the theory of general relativity. Those results suggested that anyone falling into a black hole would be burned up as they crossed its edge - the so-called event horizon.
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The Hawking Paradox - BBC Horizon

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Title: Black Hole's 1/N Hair
Authors: Gia Dvali, Cesar Gomez

According to the standard view classically black holes carry no hair, whereas quantum hair is at best exponentially weak. We show that suppression of hair is an artefact of the semi-classical treatment and that in the quantum picture hair appears as an inverse mass-square effect. Such hair is predicted in the microscopic quantum description in which a black hole represents a self-sustained leaky Bose-condensate of N soft gravitons. In this picture the Hawking radiation is the quantum depletion of the condensate. Within this picture we show that quantum black hole physics is fully compatible with continuous global symmetries and that global hair appears with the strength B/N, where B is the global charge swallowed by the black hole. For large charge this hair has dramatic effect on black hole dynamics. Our findings can have interesting astrophysical consequences, such as existence of black holes with large detectable baryonic and leptonic numbers.

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Title: On Relativistic Quantum Information Properties of Entangled Wave Vectors of Massive Fermions
Authors: C. Cafaro, S. Capozziello, S. Mancini

We study special relativistic effects on the entanglement between either spins or momenta of composite quantum systems of two spin-1/2 massive particles, either indistinguishable or distinguishable, in inertial reference frames in relative motion. For the case of indistinguishable particles, we consider a balanced scenario where the momenta of the pair are well-defined but not maximally entangled in the rest frame while the spins of the pair are described by a one-parameter (eta) family of entangled bipartite states. For the case of distinguishable particles, we consider an unbalanced scenario where the momenta of the pair are well-defined and maximally entangled in the rest frame while the spins of the pair are described by a one-parameter (xi) family of non-maximally entangled bipartite states. In both cases, we show that neither the spin-spin (ss) nor the momentum-momentum (mm) entanglements quantified by means of Wootters' concurrence are Lorentz invariant quantities: the total amount of entanglement regarded as the sum of these entanglements is not the same in different inertial moving frames. In particular, for any value of the entangling parameters, both ss and mm-entanglements are attenuated by Lorentz transformations and their parametric rates of change with respect to the entanglements observed in a rest frame have the same monotonic behaviour. However, for indistinguishable (distinguishable) particles, the change in entanglement for the momenta is (is not) the same as the change in entanglement for spins. As a consequence, in both cases, no entanglement compensation between spin and momentum degrees of freedom occurs.

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Title: Experimental Test of Quantum No-Hiding Theorem
Authors: Jharana Rani Samal, Arun Kumar Pati, Anil Kumar

The no-hiding theorem says that if any physical process leads to bleaching of quantum information from the original system, then it must reside in the rest of the Universe with no information being hidden in the correlation between these two subsystems. Here, we report an experimental test of the no-hiding theorem with the technique of nuclear magnetic resonance. We use the quantum state randomisation of a qubit as one example of the bleaching process and show that the missing information can be fully recovered up to local unitary transformations in the ancilla qubits.

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