Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session T6: Entangled States of Photons and Atoms |
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Chair: Poul Jessen, University of Arizona Room: Garden 4 |
Friday, June 8, 2012 8:00AM - 8:12AM |
T6.00001: Standard Polarization-Maintaining Fibers as a Source of Polarization-Entangled Photons Virginia Lorenz, Bin Fang, Offir Cohen, Jamy Moreno Entangled photons are a crucial resource for quantum communication, quantum computation and fundamental tests of quantum mechanics, which often require the distribution or processing of entangled photons through single-mode fiber (SMF) networks. However, coupling into SMFs has been a challenge due to the spatial mode mismatch between the created photons and the guided mode in the SMF. Recently, it was demonstrated that efficient generation of photon-pairs at visible wavelengths is possible using standard, commercially available polarization-maintaining fibers (PMFs), with high coupling efficiency into SMFs. Here we demonstrate the capability of the source to generate polarization-entangled photon-pairs by inserting a PMF source into a Sagnac interferometer. With a total pump power of 10mW of $\sim$200fs pulses at 715nm and 80MHz, we obtain 350 coincidences/s of photons at 850nm and 620nm. We perform a quantum state tomography to reconstruct the density matrix, yielding, without background subtraction, a tangle of $T=0.629\pm 0.022$, a linear entropy of $S=0.264\pm 0.014$, and a fidelity with a maximally entangled state of $90.40\pm 0.56\%$, clearly exhibiting non-classical entanglement. We expect this source to be useful for fiber-based quantum communication protocols. [Preview Abstract] |
Friday, June 8, 2012 8:12AM - 8:24AM |
T6.00002: A Miniature Ultrabright Source of Long Biphotons Chih-Sung Chuu, G.Y. Yin, Stephen E. Harris An ultrabright compact source of long biphotons is essential for scalable quantum networks. Here we report the generation of long biphotons utilizing the cluster effect in a monolithic doubly resonant parametric down-converter. The biphoton generation rate and spectral brightness are 110 and 41 times larger, respectively, than previously reported. This source will find applications in quantum repeater protocols. [Preview Abstract] |
Friday, June 8, 2012 8:24AM - 8:36AM |
T6.00003: Quantum Interference between nondegenerate entangled photons Chang Liu, J.F. Chen, Shanchao Zhang, Shuyu Zhou, Yoon-Ho Kim, M.M.T. Loy, G.K.L. Wong, Shengwang Du We generate narrow-band entangled photon pairs from laser cooled atoms in a right-angle geometry and study their Hong-Ou-Mandel (HOM) two-photon quantum interference. When the two paths are balanced before the beam splitter, we observe a perfect destructive interference for both degenerate and nondegenerate photons. In particular, our results show that the path-exchange symmetry plays a more general critical role for observing the HOM interference, rather than the temporal or frequency indistinguishability of the photons and their simultaneous arrival at the beam splitter. The interference between the indistinguishable Feynman pathways leads to the HOM effect for both degenerate and nondegenerate paired photons. Furthermore, we also show that the quantum beat between nondegenerate photons can be measured with slow detectors by varying the relative path length difference, in addition to the direct observation of the quantum beat with fast detectors in an unbalanced-path configuration. Our results may lead to potential applications in linear optical quantum information processing involving photons at different wavelengths. [Preview Abstract] |
Friday, June 8, 2012 8:36AM - 8:48AM |
T6.00004: Path Entangled Photon Number States in the Presence of Loss for Quantum Metrology Chase Brignac, Kebei Jiang, Yi Weng, Jonathan Dowling Quantum states of light have long been researched to achieve greater phase resolution and phase sensitivity than what is possible classically. In 2009 Huver found that path-entangled photon number states where there are one or more photons in each path drastically improves on the performance with loss compared to N00N states in the presence of photon loss. The amplitude of the photodetection operator applied to such states may be expressed as a function of the off- diagonal terms in the reduced density matrix. In path-entangled photon number states there are two paths a and b with different numbers of photons. We have maximized the amplitude of the expectation value of the detection operator with respect to path-entangled photon number states under loss to better understand what photon number states are optimal for practical application. [Preview Abstract] |
Friday, June 8, 2012 8:48AM - 9:00AM |
T6.00005: Quantum Cramer-Rao Bound for M\&M' States with Lossy Interferometers Yi Weng, Moochan B. Kim, Hwang Lee, Jonathan P. Dowling Understanding limits on interferometers performance is fundamental to quantum metrology. The standard quantum limit was considered as the fundamental limitation on measurements made with light beams for long. Using non-classical states of light, this precision can be improved to the Heisenberg limit. Unfortunately, highly correlated quantum states of light are very fragile with respect to noise. In 2008, Huver introduced a path-entangled number state known as M$\&$M' state, $\left|M::M^{'}\right\rangle_{a,b}=\left(\left|M,M^{'}\right\rangle_{a,b}+\left|M^{'},M\right\rangle_{a,b}\right)/\sqrt{2}$, which is more robust to loss than N00N states possessing all photons in either mode. In this talk, we give a detailed discussion of quantum states for optical two-mode interferometers with definite photon number in the presence of photon losses. We calculate an expression for the quantum Fisher information as well as the Quantum Cramer-Rao Bound for optical two-mode Interferometers of M\&M' states with loss. [Preview Abstract] |
Friday, June 8, 2012 9:00AM - 9:12AM |
T6.00006: Fringe visibility and Which-Way information for Robust Entangled Fock states Kebei Jiang, Moochan Kim, Chase Brignac, Hwang Lee, Jonathan Dowling It has been shown that mm states, a class of path-entangled Fock states which have non-zero photon numbers on both arms of a two-mode interferometer, are robust against photon loss to a certain degree. To explain the reason for such robustness we calculate which-way information, the visibility of interference fringe and the degree of entanglement for mm states in a two-mode interferometer. We go on to derive a complementarity relation between these quantities. We show that less which-way information is revealed by using mm states than N00N states. This is because of the decoyed photons which are present in both arms of the interferometer. Hence mm states provide better visibility. [Preview Abstract] |
Friday, June 8, 2012 9:12AM - 9:24AM |
T6.00007: Using a CNOT gate to improve detector efficiency Katherine Brown, Ben Fortescue, Moochan Kim, Chris Richardson, Jonathan Dowling One of the most significant problems with photonic quantum computing is that of photon loss. Unfortunately detecting, and correcting for photon loss is made considerably more difficult due to the problem of inefficient photon detectors, which often have a detection efficiency far lower than that required for standard quantum error correction. In this presentation we will consider the problem of trying to detect the state of a photon at the end of our calculation with detectors that only have an efficiency of 90{\%}. In particularly we will consider how entangling quantum gates can be used to boost the efficiency of the lossy detectors, and how this affects the accuracy of the result that can be obtained. We will compare two different procedures, one which allows us to determine whether the photon we are aiming to detect has been lost before or during the detection procedure, and the other which replaces a photon loss error with a bit flip error. This will allow us to show the trade off between detectable errors, and undetectable errors, something important to consider in quantum error correction. [Preview Abstract] |
Friday, June 8, 2012 9:24AM - 9:36AM |
T6.00008: Phase estimation with two-mode squeezed vacuum and parity detection: Bayesian analysis Keith Motes, Petr Anisimov, Jonathan Dowling Using Bayesian analysis we characterized the performance of phase estimation in the Mach-Zehnder interferometer with two-mode squeezed vacuum input. Phase uncertainty, averaged over many trials, is examined and the dependence on photon number is found. As we continue investigating our results we hope to determine the ideal average number of photons to use in a MZI with TMSV and compare it with shot-noise and Heisenberg limited sensitivity. Our scheme works well for small unknown phases but requires a large number of trials and a small number of input photons. In actual implementations of the scheme, a control phase $\psi $ has to be implemented to maintain unknown phase difference at the ``sweet spot.'' [Preview Abstract] |
Friday, June 8, 2012 9:36AM - 9:48AM |
T6.00009: Enhanced Spin Squeezing Through Quantum Control of Qudits Leigh Norris, Collin Trail, Poul Jessen, Ivan Deutsch Spin squeezed states have applications in metrology and quantum information processing. Most spin squeezing research to date has focused on ensembles of qubit spins. We explore squeezed state production in an ensemble of spin f$>$1/2 alkali atoms (qudits). Collective interactions are achieved through coherent quantum feedback of a laser probe, interacting with the ensemble through Faraday interaction. This process is enhanced with control of the atomic qudits, both before and after the collective interaction. Initial preparation increases the collective squeezing parameter through enhancement of resolvable quantum fluctuations, but comes at the price of increased decoherence. We find an optimal state preparation, achieving an increased squeezing parameter while remaining robust to decoherence. After the collective interaction, qudit control maps generated entanglement to different pseudo-spin subspaces where it is metrologically useful, e.g., the clock transition or the stretched state for magnetometry. These considerations highlight the unique capabilities of our platform: we can transfer correlations between subspaces to explore a wider variety of nonclassical states, with ultimate application in sensors or quantum information processors. [Preview Abstract] |
Friday, June 8, 2012 9:48AM - 10:00AM |
T6.00010: Towards single atoms in an optical dipole trap using Rydberg blockade X.L. Zhang, A.T. Gill, M. Gibbons, L. Zhang, L. Isenhower, T.G. Walker, M. Saffman We present experimental studies of preparation of single atom occupancy of optical dipole traps using Rydberg blockade of few atom samples. Starting with N atoms in the $F=2$ state of $^{87}$Rb we perform stimulated Raman transfers to $F=1$ via a highly excited Rydberg state. Single atom occupancy is obtained with better than 50\% probability. The results are compared with a numerical model accounting for the atomic interactions which predicts the possibility of $\sim 80\%$ single atom loading starting from samples with $N\sim 10$ atoms. [Preview Abstract] |
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