BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Vijay Balasubramanian (UPenn) DTSTART:20200507T190000Z DTEND:20200507T200000Z DTSTAMP:20260422T225759Z UID:IFQ/1 DESCRIPTION:Title: Geom etric secret sharing in a model of Hawking radiation\nby Vijay Balasub ramanian (UPenn) as part of It from Qubit\n\n\nAbstract\nWe consider a bla ck hole in three dimensional AdS space entangled with an auxiliary radiati on system. We then model the microstates of the black hole in terms of a f ield theory living on an end of the world brane behind the horizon\, and a llow this field theory to itself have a holographic dual geometry. This ge ometry is also a black hole since entanglement of the microstates with the radiation leaves them in a mixed state. This "inception black hole" can b e purified by entanglement through a wormhole with an auxiliary system whi ch is naturally identified with the external radiation\, giving a realizat ion of the ER=EPR scenario. In this context\, we propose an extension of t he Ryu-Takayanagi (RT) formula\, in which extremal surfaces computing enta nglement entropy are allowed to pass through the brane into its dual geome try. This new rule reproduces the Page curve for evaporating black holes\, consistently with the recently proposed "island formula". We then separat e the radiation system into pieces. Our extended RT rule shows that the en tanglement wedge of the union of radiation subsystems covers the black hol e interior at late times\, but the union of entanglement wedges of the sub systems may not. This result points to a secret sharing scheme in Hawking radiation wherein reconstruction of certain regions in the interior is imp ossible with any subsystem of the radiation\, but possible with all of it. \n LOCATION:https://researchseminars.org/talk/IFQ/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Hrant Gharibyan (Caltech) DTSTART:20200521T190000Z DTEND:20200521T210000Z DTSTAMP:20260422T225759Z UID:IFQ/2 DESCRIPTION:Title: The Python's Lunch: geometric obstructions to decoding Hawking radiation\n by Hrant Gharibyan (Caltech) as part of It from Qubit\n\n\nAbstract\nHarlo w and Hayden [arXiv:1301.4504] argued that distilling information out of H awking radiation is computationally hard despite the fact that the quantum state of the black hole and its radiation is relatively un-complex. I wil l trace this computational difficulty to a geometric obstruction in the Ei nstein-Rosen bridge connecting the black hole and its radiation. Inspired by tensor network models\, I will present a conjecture that relates the co mputational hardness of distilling information to geometric features of th e wormhole - specifically to the exponential of the difference in generali zed entropies between the two non-minimal quantum extremal surfaces that c onstitute the obstruction. Due to its shape\, this obstruction was dubbed "Python's Lunch"\, in analogy to the reptile's postprandial bulge.\n LOCATION:https://researchseminars.org/talk/IFQ/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Jordan Cotler (Stanford) DTSTART:20200616T200000Z DTEND:20200616T220000Z DTSTAMP:20260422T225759Z UID:IFQ/3 DESCRIPTION:Title: AdS3 gravity and random CFT\nby Jordan Cotler (Stanford) as part of It fro m Qubit\n\n\nAbstract\nWe compute the path integral of three-dimensional g ravity with negative cosmological constant on spaces which are topological ly a torus times an interval. These are Euclidean wormholes\, which smooth ly interpolate between two asymptotically Euclidean AdS3 regions with toru s boundary. From our results we obtain the spectral correlations between B TZ black hole microstates near threshold\, as well as extract the spectral form factor at fixed momentum\, which has linear growth in time with smal l fluctuations around it. The low-energy limit of these correlations is pr ecisely that of a double-scaled random matrix ensemble with Virasoro symme try. Our findings suggest that if pure three-dimensional gravity has a hol ographic dual\, then the dual is an ensemble which generalizes random matr ix theory.\n LOCATION:https://researchseminars.org/talk/IFQ/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Ying Zhao (IAS) DTSTART:20200421T200000Z DTEND:20200421T220000Z DTSTAMP:20260422T225759Z UID:IFQ/4 DESCRIPTION:Title: A qu antum circuit interpretation of evaporating black hole geometry\nby Yi ng Zhao (IAS) as part of It from Qubit\n\n\nAbstract\nWhen Alice shares th ermofield double with Bob\, her time evolution can make the wormhole grow. We identify different kinds of operations Alice can do as being responsib le for the growth of different parts of spacetime and see how it fits toge ther with subregion duality. With this\, we give a quantum circuit interpr etation of evaporating black hole geometry. We make an analogy between the appearance of island for evaporating black hole and the transition from t wo-sided to one-sided black hole in the familiar example of perturbed ther mofield double. If Alice perturbs thermofield double and waits for scrambl ing time\, she will have a one-sided black hole with interior of her own. We argue that by similar mechanism the radiation gets access to the interi or (island forms) after Page time. The growth of the island happens as a r esult of the constant transitions from two-sided to one-sided black holes. \n LOCATION:https://researchseminars.org/talk/IFQ/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Don Marolf (UCSB) DTSTART:20200409T203000Z DTEND:20200409T223000Z DTSTAMP:20260422T225759Z UID:IFQ/5 DESCRIPTION:Title: Baby Universes and Black Hole Information\nby Don Marolf (UCSB) as part of It from Qubit\n\n\nAbstract\nIn the 1980’s\, work by Coleman and by Gid dings and Strominger linked the physics of spacetime wormholes to ‘baby universes’ and an ensemble of theories. We revisit such ideas\, using fe atures associated with a negative cosmological constant and asymptotically AdS boundaries to strengthen the results\, introduce a change in perspect ive\, and connect with recent replica wormhole discussions of the Page cur ve. A key new feature is an emphasis on the role of null states. We explor e this structure in detail in simple topological models of the bulk that a llow us to compute the full spectrum of associated boundary theories. We also argue that similar properties must hold in any consistent gravitation al path integral.\n LOCATION:https://researchseminars.org/talk/IFQ/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Hong Liu (MIT) DTSTART:20200716T190000Z DTEND:20200716T210000Z DTSTAMP:20260422T225759Z UID:IFQ/6 DESCRIPTION:Title: Enta nglement entropies of equilibrated pure states and replica wormholes\n by Hong Liu (MIT) as part of It from Qubit\n\n\nAbstract\nConsider a quant um many-body system initially in a far-from-equilibrium pure state.\n\nIf the system is non-integrable\, the state should approach equilibrium after some time.\n\nWe develop an approximation to calculate quantum informatio nal properties of such an "equilibrated pure state.” Applied to gravity systems\, the approximation leads to a derivation of replica wormholes di scussed recently in the context of Page curves for black holes\, elucidati ng their mathematical origin\, physical interpretation\, and why they lea d to answers which are consistent with unitarity.\n\nBased on work to appe ar with Shreya Vardhan.\n LOCATION:https://researchseminars.org/talk/IFQ/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Pablo Bueno (Instituto Balseiro\, Bariloche) DTSTART:20201021T190000Z DTEND:20201021T201500Z DTSTAMP:20260422T225759Z UID:IFQ/7 DESCRIPTION:Title: Refl ected entropy\, free fields and symmetries\nby Pablo Bueno (Instituto Balseiro\, Bariloche) as part of It from Qubit\n\n\nAbstract\nA well-defin ed notion of von Neumann entropy associated to pairs of spatial subregions has been recently proposed both in the holographic context and for genera l QFTs. I will show that in the case of Gaussian systems ---and similarly to the entanglement entropy (EE)--- this "reflected entropy” can be obta ined in terms of correlation functions of the fields. In particular\, I wi ll present general formulas valid for free scalars and fermions in arbitra ry dimensions. I will apply the results to various free theories in 1+1 an d 2+1 dimensions\, verifying that the conjectural monotonicity property $R (A\,BC)\\geq R(A\,B)$ and the general inequality $R(A\,B)\\geq I(A\,B)$ ho ld in all cases. The results obtained suggest that for general regions cha racterized by length-scales $L_A\\sim L_B \\sim L$ and separated a distanc e $\\ell$\, the reflected entropy in the large-separation regime ($x\\equi v L/\\ell \\ll 1$) is related to the mutual information by: $R(x) \\sim −I(x) \\log x$ for general CFTs in arbitrary dimensions. Finally\, I wil l argue that the notion of reflected entropy can be canonically generalize d in a way which is particularly suitable for theories obtained by restric ting the full algebra of operators to those which are neutral under global symmetry groups. A key role in the discussion is played by type-I von Neu mann algebras\, which differ from the usual type-III algebras associated t o spatial subregions in QFT. I will perform various explicit comparisons b etween both types of algebras.\n LOCATION:https://researchseminars.org/talk/IFQ/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Jafferis (Harvard) DTSTART:20201113T190000Z DTEND:20201113T210000Z DTSTAMP:20260422T225759Z UID:IFQ/8 DESCRIPTION:Title: Insi de the Hologram\nby Daniel Jafferis (Harvard) as part of It from Qubit \n\n\nAbstract\nI will discuss using probe black holes to explore the reco nstruction of bulk operators. Under some assumptions\, modular flow of the probes evolves nearby bulk operators in proper time along the probe traje ctory. This includes cases where the evolution goes behind horizons in the spacetime being probed.\n LOCATION:https://researchseminars.org/talk/IFQ/8/ END:VEVENT END:VCALENDAR