Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session M5: Quantum Control I |
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Chair: Seth Aubin, College of William and Mary Room: 551AB |
Thursday, May 26, 2016 8:00AM - 8:12AM |
M5.00001: Carving Complex Many-Atom Entangled States by Single-Photon Detection Wenlan Chen, Jiazhong Hu, Yiheng Duan, Boris Braverman, Hao Zhang, Vladan Vuletic We propose a versatile and efficient method to generate a broad class of complex entangled states of many atoms via the detection of a single photon. For an atomic ensemble contained in a strongly coupled optical cavity illuminated by weak single- or multifrequency light, the atom-light interaction entangles the frequency spectrum of a transmitted photon with the collective spin of the atomic ensemble. Simple time-resolved detection of the transmitted photon then projects the atomic ensemble into a desired pure entangled state. This method can be implemented with existing technology, yields high success probability per trial, and can generate complex entangled states such as mesoscopic superposition states of coherent spin states with high fidelity. [Preview Abstract] |
Thursday, May 26, 2016 8:12AM - 8:24AM |
M5.00002: Generating and probing entangled states for optical atomic clocks Boris Braverman, Akio Kawasaki, Vladan Vuletic The precision of quantum measurements is inherently limited by projection noise caused by the measurement process itself. Spin squeezing and more complex forms of entanglement have been proposed as ways of surpassing this limitation. In our system, a high-finesse asymmetric micromirror-based optical cavity can mediate the atom-atom interaction necessary for generating entanglement in an ${}^{171}$Yb optical lattice clock. I will discuss approaches for creating, characterizing, and optimally utilizing these nonclassical states for precision measurement, as well as recent progress toward their realization. [Preview Abstract] |
Thursday, May 26, 2016 8:24AM - 8:36AM |
M5.00003: Generation of single photons with highly tunable wave shape from a cold atomic quantum memory Georg Heinze, Pau Farrera, Boris Albrecht, Hugues de Riedmatten, Melvyn Ho, Matias Chavez, Colin Teo, Nicolas Sangouard We report on a single photon source with highly tunable photon shape based on a cold ensemble of Rubidium atoms [1]. We follow the DLCZ scheme [2] to implement an emissive quantum memory, which can be operated as a photon pair source with controllable delay. We find that the temporal wave shape of the emitted read photon can be precisely controlled by changing the shape of the driving read pulse. We generate photons with temporal durations varying over three orders of magnitude up to $10\,\mu\mathrm{s}$ without a significant change of the read-out efficiency. We prove the non-classicality of the emitted photons by measuring their antibunching, showing near single photon behavior at low excitation probabilities. We also show that the photons are emitted in a pure state by measuring unconditional autocorrelation functions. Finally, to demonstrate the usability of the source for realistic applications, we create ultra-long single photons with a rising exponential or doubly peaked time-bin wave shape which are important for several quantum information tasks.\\ {[1]} P. Farrera {\it et~al.}, arXiv:1601.07142 (2016).\\ {[2]} L.~M. Duan {\it et~al.}, Nature {\bf 414}, 413 (2001). [Preview Abstract] |
Thursday, May 26, 2016 8:36AM - 8:48AM |
M5.00004: Improved spin squeezing of an atomic ensemble through internal state control Daniel Hemmer, Enrique Montano, Ivan Deutsch, Poul Jessen Squeezing of collective atomic spins is typically generated by quantum backaction from a QND measurement of the relevant spin component. In this scenario the degree of squeezing is determined by the measurement resolution relative to the quantum projection noise (QPN) of a spin coherent state (SCS). Greater squeezing can be achieved through optimization of the 3D geometry of probe and atom cloud, or by placing the atoms in an optical cavity. We explore here a complementary strategy that relies on quantum control of the large internal spin available in alkali atoms such as Cs. Using a combination of rf and uw magnetic fields, we coherently map the internal spins in our ensemble from the SCS (\textbar $f=$4,$m=$4\textgreater ) to a "cat" state which is an equal superposition of \textbar $f=$4, $m=$4\textgreater and \textbar $f=$4, $m=$-4\textgreater . This increases QPN by a factor of 2$f=$8 relative to the SCS, and therefore the amount of backaction and spin-spin entanglement produced by our QND measurement. In a final step, squeezing generated in the cat state basis can be mapped back to the SCS basis, where it corresponds to increased squeezing of the physical spin. Our experiments suggest that up to 8dB of metrologically useful squeezing can be generated in this way, compared to \textasciitilde 3dB in an otherwise identical experiment starting from a SCS. [Preview Abstract] |
Thursday, May 26, 2016 8:48AM - 9:00AM |
M5.00005: Direct Experimental Observation of a Practical AC Zeeman Force Charles Fancher, Andrew Pyle, Andrew Rotunno, ShuangLi Du, Seth Aubin We present measurements of the spin-dependent AC Zeeman force produced by microwave magnetic near-field gradients on an atom chip. We measure the AC Zeeman force on ultracold $^{87}$Rb atoms by observing its effect on the motion of atoms in free-fall and on those confined in a trap. We have studied the force as a function of microwave frequency detuning from a hyperfine transition at 6.8 GHz at several magnetic field strengths and have observed its characteristic bipolar and resonant features predicted by two-level dressed atom theory. We find that the force is several times the strength of gravity in our setup, and that it can be targeted to a specific hyperfine transition while leaving other hyperfine states and transitions relatively unaffected. We find that our measurements are reasonably consistent with theory and are working towards a parameter-free comparison. AC Zeeman potentials offer the possibility of targeting qualitatively different trapping potentials to different spin states, a capability currently absent from the toolbox of atomic quantum control techniques. In particular, an AC Zeeman potential could be used as the beamsplitter for a spin-dependent atom interferometer or for engineering a quantum gate. [Preview Abstract] |
Thursday, May 26, 2016 9:00AM - 9:12AM |
M5.00006: Sympathetic cooling of $^{\mathrm{171}}$Yb$^{\mathrm{+}}$ qubit ions on a scalable ion trap chip using Yb isotopes Yeong-Dae Kwon, Jun Sik Ahn, Seokjun Hong, Minjae Lee, Hongjin Cheon, Dongil ”Dan” Cho, Taehyun Kim To achieve ion trap based large-scale quantum computing devices, motional states of qubit ions must be regulated against heating from ion transportation or noise on the chip surface while leaving internal states of the ions intact. Sympathetic cooling is a natural solution for this problem, but trapping two different species of ions generally requires two sets of optical devices including separate lasers for each ion type, increasing the complexity and the cost of the setup. We tested Doppler-cooled $^{\mathrm{174}}$Yb$^{\mathrm{+}}$ ions to sympathetically cool $^{\mathrm{171}}$Yb$^{\mathrm{+}}$ qubit ions. Since these two isotopes have energy levels close to each other, the optical setup can be vastly simplified. We also verified that the tail of non-ideally focused cooling beam and the scattered light from the surface create excited state population in the $^{\mathrm{171}}$Yb$^{\mathrm{+}}$ qubit ions, as expected. This leads to occasional spontaneous emission events, which currently limits the coherence time of our qubit to a few seconds. We will also discuss our plans for optimizing the experiment, which may increase the coherence time by one or two orders of magnitude. [Preview Abstract] |
Thursday, May 26, 2016 9:12AM - 9:24AM |
M5.00007: Long coherence time of an ion memory in a hybrid ion trap Ye Wang, Dahyun Yum, Ming Lyu, Shuoming An, Mark Um, Junhua Zhang, Luming Duan, Kihwan Kim For an ensemble of qubits, there have reports of hours-long coherence time in both trapped ions [1] and solid state systems [2]. For a single qubit, however, the longest reported coherence time is about tens of seconds [3], which is mainly limited by the heating of the ion. We have performed an experiment to increase the coherence time of an ion qubit to a few minutes through dynamical decoupling. Our experiment is done in a hybrid ion trap, with 171Yb$+$ as the memory ion qubit and 138Ba$+$ as the cooling ion. Both of the ions are kept near their motional ground state through sympathetic cooling. The coherence time in our system is mainly limited by the gate fidelity for the dynamical decoupling pulses and the low frequency noise. [1] J. J. Bollinger, et al., IEEE Trans. Instrum. Meas. 40, 126 (1991). [2]Manjin Zhong, et al., Nature 517, 177 (2015). [3] T. P. Harty, et al., Phys. Rev. Lett. 113, 220501 (2014). [Preview Abstract] |
Thursday, May 26, 2016 9:24AM - 9:36AM |
M5.00008: ABSTRACT WITHDRAWN |
Thursday, May 26, 2016 9:36AM - 9:48AM |
M5.00009: High resolution quantum metrology via quantum interpolation Ashok Ajoy, YiXiang Liu, Kasturi Saha, Luca Marseglia, Jean-Christophe Jaskula, Paola Cappellaro Nitrogen Vacancy (NV) centers in diamond are a promising platform for quantum metrology -- in particular for nanoscale magnetic resonance imaging to determine high resolution structures of single molecules placed outside the diamond. The conventional technique for sensing of external nuclear spins involves monitoring the effects of the target nuclear spins on the NV center coherence under dynamical decoupling (the CPMG/XY8 pulse sequence). However, the nuclear spin affects the NV coherence only at precise free evolution times -- and finite timing resolution set by hardware often severely limits the sensitivity and resolution of the method. In this work, we overcome this timing resolution barrier by developing a technique to supersample the metrology signal by effectively implementing a quantum interpolation of the spin system dynamics. This method will enable spin sensing at high magnetic fields and high repetition rate, allowing significant improvements in sensitivity and spectral resolution. We experimentally demonstrate a resolution boost by over a factor of 100 for spin sensing and AC magnetometry. The method is shown to be robust, versatile to sensing normal and spurious signal harmonics, and ultimately limited in resolution only by the number of pulses that can be applied [Preview Abstract] |
Thursday, May 26, 2016 9:48AM - 10:00AM |
M5.00010: Tunable coupling between two electronic spin qubits in diamond Junghyun Lee, Keigo Arai, Huiliang Zhang, Erik Bauch, Emma Rosenfeld, Mikael Backlund, Ronald Walsworth Nitrogen-vacancy (NV) color centers in diamond are good candidates for realizing a scalable spin coupled system. For a simple two NV electronic spin interacting system, spin polarization can be transferred from one spin to another spin through the spin dipolar interaction. With two NV electronic spins separated by about 10 nm, and by manipulating an applied magnetic field gradient and a Rabi driving field, we outline how the spin dipolar interaction can be controlled, with observable changes in the dominating interaction dynamics. Furthermore, we discuss how this control scheme can be applied to transfer polarization in a strongly-coupled spin-chain system. [Preview Abstract] |
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