*ITAMP Topical Lunch Discussion* Date: Thursday, March 3rd Time: 12:00-1:30 pm Pizza will be served. Location: B-106 @ Center for Astrophysics (60 Garden Street) Directions: after entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, and B-106 is there. *Speaker:* Robert Fickler(University of Ottawa) *Title:*Twisted Photon Entanglement with 10010 Quanta and over large Distances *Abstract: * Photons with twisted phase-fronts can carry an (theoretically) unbounded amount of orbital angular momentum (OAM), which corresponds to a large state space for encoding quantum information. They can be used as laboratory realization of high-dimensional quantum states, which are known to be advantageous in quantum information schemes, e.g. quantum cryptography. Additionally, twisted photons are of fundamental interest to test how much information a single quantum system can carry, how large the dimensionality of entanglement can be or to challenge possible limits of quantum mechanical predictions. In a first experiment, we investigate the latter one by exploring how many quanta of orbital angular momentum an entangled photon pair allows. We employ a novel technique that is able to generate photons with unprecedented high quanta of OAM by reflecting them from a mirror with a surface profile corresponding to the required helical phase. With this we are able to entangle up to ±10010 quanta of OAM of one photon with the polarization of its partner, thereby realizing a quantum experiment involving the largest quantum number so far (to our knowledge). In a second experiment, we investigate the possibility of distributing OAM entangled photons over long distances. Despite pessimistic theoretical predictions, we experimentally demonstrate the successful distribution of entanglement encoded in OAM through a turbulent intra-city link of 3 kilometers. Here, we are able to verify entanglement of photons carrying up to ±2 OAM quanta and show the capability of our setup to distribute at least 11 orthogonal quantum channels. -- Dr. Igor Pikovski Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) Harvard-Smithsonian Center for Astrophysics 60 Garden St, MS-14; Cambridge, MA 02138, USA Tel.: +1 (617) 496-7613 e-mail: igor.pikovski(a)cfa.harvard.edu www.cfa.harvard.edu/~igor.pikovski/

*ITAMP Topical Lunch Discussion* *Speaker:* Ivar Zapata (Universidad Complutense de Madrid) *Title:* Connection of separate Bose-Einstein condensates via Josephson effect *Abstract: *This work is about the dynamics of the relative phase following a Josephson link between two independently formed Bose-Einstein condensates. The effect of Bogoliubov excitations on the coherence properties of the relative phase is evaluated in a semiclassical regime, in which the system undergoes Bloch oscillations around the initial particle number. This allows a description of decoherence in terms of energy relaxation. The method used is explained so that it could be extended to other related fields, specially polaron physics. Date: Thursday, March 17th Time: 12:00-1:30 pm Pizza will be served. Location: B-106 @ Center for Astrophysics (60 Garden Street) Directions: after entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, and B-106 is there. -- Dr. Igor Pikovski Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) Harvard-Smithsonian Center for Astrophysics 60 Garden St, MS-14; Cambridge, MA 02138, USA Tel.: +1 (617) 496-7613 e-mail: igor.pikovski(a)cfa.harvard.edu www.cfa.harvard.edu/~igor.pikovski/

*ITAMP Topical Lunch Discussion* *Speaker:* Shimon Kolkowitz (NIST / JILA / University of Colorado, Boulder) *Title:* Prospects for quantum simulation and gravitational wave detection with optical lattice clocks *Abstract: *Optical atomic clocks are now the most stable and accurate timekeepers in the world, operating with fractional accuracies and stabilities at the 10-18 level. Neutral atom optical lattice clocks offer the intriguing prospect of harnessing this precision for the investigation of quantum many-body physics. Here we present experimental progress towards the generation and study of spin-orbit coupling in a strontium optical lattice clock. We utilize an unbalanced 1D horizontal lattice to realize tunable tunneling while maintaining strong radial confinement, and take advantage of the sensitivity afforded by the clock transition to probe the influence of many-body interactions on the engineered Hamiltonian. We present the first experimental signatures of spin-orbit coupling in our lattice clock. We will also present a proposal for a novel gravitational wave detector composed of space-borne optical lattice clocks. *Date:* Thursday, March 31st *Time:* 12:00-1:30 pm Pizza will be served. *Location:* B-106 @ Center for Astrophysics (60 Garden Street) Directions: after entering the lobby of the CfA, turn right to enter the hallway of the B building. In the hallway, turn right again, and B-106 is there. -- Dr. Igor Pikovski Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) Harvard-Smithsonian Center for Astrophysics 60 Garden St, MS-14; Cambridge, MA 02138, USA Tel.: +1 (617) 496-7613 e-mail: igor.pikovski(a)cfa.harvard.edu www.cfa.harvard.edu/~igor.pikovski/

*ITAMP Seminar * *Speaker:* Prof. Martin Schaden (Rutgers University) *Title:* Causal Space-Times on a Null Lattice (based on arXiv:1509.03095v2) *Abstract: *I propose a discrete model of Quantum Gravity based on the same principle as the Global Positioning System: the intersection of forward light-cones from four spatially separate events (with certain restrictions) determines another event. I show that causal manifold can thus be triangulated by a topologically hypercubic lattice with light-like links; the length of the spatial diagonal of each plaquette being determined by spinors describing its light-like edges. This lattice model has an SL(2,C) x U^4(1) structure group and is geometric. The description foliates in a causal and physically transparent manner. The observables, the most general local action and the integration measure of this model are all derived from this stucture group and for smooth configurations have well-known continuum limits. Consistency constraints on a configuration to describe the triangulation of a causal manifold are derived and a one-parameter ambiguity of the invariant integration measure is exploited to regularize the model. Finally its SL(2,C) structure group is uniquely (without Gribov ambiguity) localized and the integration measure expressed in terms of geometrical invariants. Should time and interest permit, I will discuss global issues and show numerical results on a small lattice describing the vicinity of the Big Bang in the (unphysical) limit where the cosmological term dominates the dynamics. *Date:* Monday, April 11th *Time:* 3pm-4pm *Location:* Pratt Seminar Room (P-G03,4) @ Center for Astrophysics (60 Garden Street) -- Dr. Igor Pikovski Institute for Theoretical Atomic, Molecular and Optical Physics (ITAMP) Harvard-Smithsonian Center for Astrophysics 60 Garden St, MS-14; Cambridge, MA 02138, USA Tel.: +1 (617) 496-7613 e-mail: igor.pikovski(a)cfa.harvard.edu www.cfa.harvard.edu/~igor.pikovski/