Program
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SESSION 9a: AMO theory and applications (Lumpkins Ballroom South)Chair: (Rafael Alexander (University of New Mexico)) | |
| 3:45pm-4:15pm | Jason Twamley, Macquarie University Generating non-classical states of motion using spontaneous emission | Abstract. The generation of non-classical states of motion of matter is interesting both from a fundamental quantum science viewpoint but also permits such non-classical quantum states as potential resources for various quantum tasks such as quantum teleportation, sensing, communication and computation. In this work, using the SLH formalism, we explore systems of two-level emitters which are initially excited and are motionally trapped and optically coupled to a 1D waveguide either directly or via optical cavities. The emitter suffers a motional recoil upon the emission of a photon and this entangles the motion of the emitter with the emitted photon pulse. We find that for an emitter either directly coupled to a 1D waveguide, or coupled within a Fabry-Perot type cavity defined within the waveguide, the emitter is left in a mixed motional state which is typically classical (i.e. possesses a Wigner function which is positive). Interestingly, we find situations, e.g. emitter in front of a mirror, where the emitter is left in a mixed but highly non-classical motional state. We hypothesize that such non-classicality can only be achieved if the atom can re-interact with the emitted photon field. We also discover subtleties in the application of the SLH formalism to situations where the photon field can become trapped in the optical network. |
| 4:15pm-4:45pm | Swati Singh, Williams College Detecting continuous gravitational waves with superfluid helium | Abstract. Direct detection of gravitational waves is opening a new window onto our universe. Here, we study the sensitivity to continuous-wave strain fields of a kg-scale optomechanical system formed by the acoustic motion of superfluid helium-4 parametrically coupled to a superconducting microwave cavity. This narrowband detection scheme can operate at very high Q-factors, while the resonant frequency is tunable through pressurization of the helium in the 0.1-1.5 kHz range. The detector can therefore be tuned to a variety of astrophysical sources and can remain sensitive to a particular source over a long period of time. For thermal noise limited sensitivity, we find that strain fields on the order of \(h\sim {10}^{-23}/\sqrt{\mathrm{Hz}}\) are detectable. Measuring such strains is possible by implementing state of the art microwave transducer technology. We show that the proposed system can compete with interferometric detectors and potentially surpass the gravitational strain limits set by them for certain pulsar sources within a few months of integration time. |
| 4:45pm-5:15pm | David Feder, University of Calgary The Fermi-Hubbard model for universal quantum computation | Abstract. Quantum circuits based only on matchgates are able to perform non-trivial (but not universal) quantum algorithms. Because matchgates can be mapped to non-interacting fermions, these circuits can be efficiently simulated on a classical computer. One can perform universal quantum computation by adding any non-matchgate parity-preserving gate, implying that interacting fermions could be natural candidates for universal quantum computation within the circuit model. Most work to date has focused on Majorana fermions, which are difficult to realize in the laboratory. We instead explore both spinless (spin-polarized) and spin-1/2 fermions within the context of matchgate circuits, investigating interactions within a family of Fermi-Hubbard Hamiltonians, to obtain experimentally realizable conditions under which interacting fermions are able to perform universal quantum computation. |
| 5:15pm-5:45pm | Ezad Shojaee, University of New Mexico Realizing the optimal tomography through a sequence of collective weak measurements | Abstract. Abstract: In their seminal 1995 paper, Massar and Popescu proved that, given N-copies of an unknown pure qubit, the best strategy to reconstruct its state (without any adaptive feedback) is to do a collective measurement on the ensemble [1]. The optimal fidelity with which one can reconstruct the state of a pure qubit is (N+1)/(N+2) averaged over all unknown states and measurement outcomes. This can be achieved through a POVM whose measurement outcomes are spin coherent states of the collective spin J=N/2. In this work, we prove that we can realize this optimal measurement through a sequence of weak measurements of the collective spin along random directions on the sphere. Numerical evidence supports this result, and shows that we saturate the optimal fidelity for quantum state tomography averaged over all unknown states. We discuss the connection between this protocol and tomography via continuous weak measurement in the presence of time-dependent control [2]. [1] S. Massar and S. Popescu, Phys. Rev. Lett. 74, 1259 (1995). [2] A. Silberfarb, P. S. Jessen, and I. H. Deutsch Phys. Rev. Lett. 95, 030402 (2005); C. A. Riofrio, P. S. Jessen, and I. H. Deutsch, J. Phys. B: At. Mol. Opt. Phys. 44, 154007 (2011). |
| 5:45pm - 6:15 pm | Davide Girolami, Los Alamos National Laboratory Detecting metrologically useful asymmetry and entanglement by a few local measurements | Abstract. Important properties of a quantum system are not directly measurable, but they can be disclosed by how fast the system changes under controlled perturbations. In particular, asymmetry and entanglement can be verified by reconstructing the state of a quantum system. Yet, this usually requires experimental and computational resources which increase exponentially with the system size. Here we show how to detect metrologically useful asymmetry and entanglement by a limited number of measurements. This is achieved by studying how they affect the speed of evolution of a system under a unitary transformation. We show that the speed of multiqubit systems can be evaluated by measuring a set of local observables, providing exponential advantage with respect to state tomography. Indeed, the presented method requires neither the knowledge of the state and the parameter-encoding Hamiltonian nor global measurements performed on all the constituent subsystems. We implement the detection scheme in an all-optical experiment. References: Phys. Rev. Lett. 113, 170401 (2014); Phys. Rev. A 96, 042327 (2017). |
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SQuInT Chief Organizer
Akimasa Miyake, Assistant Professor
amiyake@unm.edu
SQuInT Co-Organizer
Mark M. Wilde, Assistant Professor LSU
mwilde@phys.lsu.edu
SQuInT Administrator
Gloria Cordova
gjcordo1@unm.edu
505 277-1850
SQuInT Founder
Ivan Deutsch, Regents' Professor
ideutsch@unm.edu
