SESSION 9a: Quantum control, simulation, and application (Pavilion II - III)Chair: Elohim Becerra (New Mexico)
|4:00 pm - 4:30 pm||Dylan Gorman, Häffner group (UC Berkeley)|
Quantum simulation of spin-bath dynamics with trapped ions
Abstract. Chains of trapped ions are an ideal platform for studying the dynamics of qubits coupled to bosonic environments. This kind of dynamics is of interest in many current problems in physics and biology such as charge transport, photosynthesis, and olfaction. In a chain of N trapped ions, an experimenter has access to an environment of the 3N vibrational modes of the chain, allowing for the simulation of very large vibrational environments with tunable spectral properties. In addition, the ions also serve as qubits, and both qubit-qubit and qubit-bath interactions can be engineered via quantum gates. Here, we discuss recent experimental progress investigating spin-bath dynamics in ion strings. We explore what happens as the spin-bath coupling is varied, as well as when the thermal occupation and quantum state of the environment is varied.
|4:30 pm - 5:00 pm||Tyler Keating, Biedermann-Deutsch group (New Mexico/Sandia)|
Arbitrary Dicke-state control of symmetric Rydberg ensembles
Abstract. The Rydberg blockade is a versatile tool for quantum information in neutral atoms. While the blockade is, at its heart, a two-body effect, it can be naturally used to generate many-body entanglement by creating single, collective excitations across ensembles of atoms. Given a strong blockade, such an ensemble is isomorphic to the Jaynes-Cummings model (JCM): the presence/absence of a Rydberg excitation plays the role of a qubit, while the atoms' hyperfine ground states take the place of photons. By applying symmetric raman transitions to a blockaded ensemble, we can generate SU(2) rotations on the "photon number" degree of freedom; this gives a control Hamiltonian with no clear analogue in a cavity-based JCM. We show that such raman transitions, along with Rydberg excitation, make the system controllable within its symmetric subspace. Arbitrary, symmetric n-body states can therefore be produced, including highly entangled Dicke and cat states. Depending on the laser powers and detunings used, one can control either the complete (2n+1)-dimensional symmetric space or just the (n+1)-dimensional dressed-ground manifold. We discuss the advantages and disadvantages of each, and show simulated entanglement generation among 7 atoms in both regimes. For a wide range of parameters, the time required to generate maximal entanglement is independent of atom number, so this technique could be especially useful for rapidly entangling large ensembles.
|5:00 pm - 5:30 pm||Denis Seletskiy, (Konstanz)|
Sub-cycle quantum optics: Direct sampling of vacuum fluctuations in experiment and theory
Abstract. Study and manipulation of the ground state of the radiation field is one of the central subjects in quantum optics. In a typical approach of homodyne detection, the information is averaged over multiple cycles of light and amplification to finite intensity is necessary. We demonstrate direct detection of the vacuum fluctuations of the local electric field amplitude in free space via the linear Pockels effect. Broadband electro-optic sampling with gate pulses shorter than 6 femtoseconds enables quantum-statistic readout . Distinction from the detector shot noise is achieved by modification of the sampled space-time volume, defined by an effective temporal duration and the spatial extent of the pulse in the electro-optic medium [1,2]. Ensuring an optimal detection bandwidth which matches the center frequency, here 70 THz, maximizes the vacuum amplitude since the ground-state energy approaches half a photon per optical cycle. The determined magnitude of the vacuum field  is in excellent agreement with paraxial theory . Sub-cycle resolution of the oscillating noise in the field quadrature with substantial excursions below the bare vacuum level is predicted  and currently explored in the laboratory. Our collective findings open up a new avenue to quantum analysis and manipulation of light in the extreme time-domain limit ensuring sub-cycle access to the electric-field quadrature.  C. Riek et al, Science 350, 420 (2015).  A. S. Moskalenko et al., arXiv:1508.06953, accepted in PRL
|5:30 pm - 6:00 pm||Sarah Kaiser, Jennewein group (IQC, Waterloo)|
Towards satellite-based quantum communication: field testing the QEYSSAT payload
Abstract. Long-distance quantum communication systems are of interest for commercial and fundamental scientific projects. Currently, the link length of these systems is limited by optical fiber losses or free-space line of sight. Our goal is to use low earth orbit satellites as a relay, enabling distant locations to establish a link and exchange quantum systems, including those that were too far apart to link previously. In this talk, I will describe our progress towards a proposed quantum receiver satellite payload that has a passive polarization analyzer to detect photons sent from ground stations. We have designed and constructed prototypes of the QEYSSAT (Quantum EncrYption and Science SATellite) payload with commercial and government assistance. These prototypes comprise almost the entire system needed for a form-fit-function payload and ground station. I will present tests of our system in realistic scenarios representing the environments it will face. In particular, I will present the latest results of testing this system in an aircraft. Finally, I will also identify remaining challenges for practical long distance quantum communication.
|6:00 pm - 6:30 pm||Itay Hen, (Southern California)|
Quantum annealing for constrained optimization
Abstract. Recent advances in quantum technology have led to the development and manufacturing of experimental programmable quantum annealers that could potentially solve certain quadratic unconstrained binary optimization problems faster than their classical analogues. The applicability of such devices for many theoretical and practical optimization problems, which are often constrained, is severely limited by the sparse, rigid layout of the devices' quantum bits. Traditionally, constraints are addressed by the addition of penalty terms to the Hamiltonian of the problem, which in turn requires prohibitively increasing physical resources while also restricting the dynamical range of the interactions. Here we propose a method for encoding constrained optimization problems on quantum annealers that eliminates the need for penalty terms and thereby removes many of the obstacles associated with the implementation of these. We argue the advantages of the proposed technique and illustrate its effectiveness. We then conclude by discussing the experimental feasibility of the suggested method as well as its potential to boost the encodability of other optimization problems.