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Register a new userDisconnecting a Traversable Wormhole: Universal Quench Dynamics in Random Spin Models
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Understanding strongly interacting quantum matter and quantum gravity are both important open issues in theoretical physics, and the holographic duality between quantum field theory and gravity theory nicely brings these two topics together. Nevertheless, direct connections between gravity physics and experimental observations in quantum matter are still rare. Here we utilize the gravity physics picture to understand quench dynamics experimentally observed in a class of random spin models realized in several different quantum systems, where the dynamics of magnetization are measured after the external polarization field is suddenly turned off. Two universal features of the magnetization dynamics, namely, a slow decay described by a stretched exponential function and an oscillatory behavior, are respectively found in different parameter regimes across different systems. This work addresses the issues of generic conditions under which these two universal features can occur, and we find that a natural answer to this question emerges in the gravity picture. By the holographic duality bridged by a model proposed by Maldacena and Qi, the quench dynamics after suddenly turning off the external polarization field is mapped to disconnecting an eternal traversable wormhole. Our studies show that insight from gravity physics can help unifying different experiments in quantum systems.
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Quantum effects can stabilize wormhole solutions in general relativity, allowing information and matter to be transported between two connected spacetimes. Here we study the revival dynamics of signals sent between two weakly coupled quantum chaotic systems, represented as identical Sachdev-Ye-Kitaev models, that realize holographically a traversable wormhole in anti-de Sitter spacetime AdS$_2$ for large number $N$ of particles. In this limit we find clear signatures of wormhole behavior: an excitation created in one system is quickly scrambled under its unitary dynamics, and is reassembled in the other system after a characteristic time consistent with holography predictions. This leads to revival oscillations that at low but finite temperature decay as a power-law in time. For small $N$ we also observe revivals and show that they arise from a different, non-gravitational mechanism.
The Maldacena-Qi model describes two copies of the Sachdev-Ye-Kitaev model coupled with an additional coupling, and is dual to the Jackiw-Teitelboim gravity which exhibits an eternal traversable wormhole in the low-temperature limit. In this work, we study an experimental consequence of the existence of the traversable wormhole by considering the tunneling spectroscopy for the Maldacena-Qi model. Comparing to the high-temperature black hole phase where the bulk geometry is disconnected, we find that both the tunneling probability and the differential conductance in the low-temperature wormhole phase show non-trivial oscillation, which directly provides an unambiguous signature of the underlying $operatorname{SL}(2)$ symmetry of the bulk geometry. We also perform bulk calculations in both high and low-temperature phases, which match the results from the boundary quantum theory.
Transport of strongly interacting fermions governs modern materials -- from the high-$T_c$ cuprates to bilayer graphene --, but also nuclear fission, the merging of neutron stars and the expansion of the early universe. Here we observe a universal quantum limit of diffusivity in a homogeneous, strongly interacting Fermi gas of atoms by studying sound propagation and its attenuation via the coupled transport of momentum and heat. In the normal state, the sound diffusivity ${D}$ monotonically decreases upon lowering the temperature $T$, in contrast to the diverging behavior of weakly interacting Fermi liquids. As the superfluid transition temperature is crossed, ${D}$ attains a universal value set by the ratio of Plancks constant ${h}$ and the particle mass ${m}$. This finding of quantum limited sound diffusivity informs theories of fermion transport, with relevance for hydrodynamic flow of electrons, neutrons and quarks.
A possible candidate for the present accelerated expansion of the Universe is phantom energy, which possesses an equation of state of the form $omegaequiv p/rho<-1$, consequently violating the null energy condition. As this is the fundamental ingredient to sustain traversable wormholes, this cosmic fluid presents us with a natural scenario for the existence of these exotic geometries. In this context, we shall construct phantom wormhole geometries by matching an interior wormhole solution, governed by the phantom energy equation of state, to an exterior vacuum at a junction interface. Several physical properties and characteristics of these solutions are further investigated. The dynamical stability of the transition layer of these phantom wormholes to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that the respective stable equilibrium configurations may be increased by strategically varying the wormhole throat radius.
We construct a nearly-$AdS_2$ solution describing an eternal traversable wormhole. The solution contains negative null energy generated by quantum fields under the influence of an external coupling between the two boundaries. In parallel, we discuss two SYK systems coupled by a relevant interaction. The physics of the two cases is very similar. They both share a gravitational subsector which is identical. The solution within this subsector sets the stage for dynamics which is almost conformal invariant. We study this system in detail, both in gravity and in the SYK model. The coupled SYK models have an interesting phase diagram at finite temperature, displaying the usual Hawking-Page transition between the thermal AdS phase at low temperature and the black hole phase at high temperature. Interestingly, these two phases are continuously connected in the microcannonical ensemble.
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