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K Bergmann - One of the best experts on this subject based on the ideXlab platform.

  • amplitude and phase control of a Coherent Superposition of degenerate states i theory
    Physical Review A, 2007
    Co-Authors: Frank Vewinger, B W Shore, Manfred Heinz, K Bergmann
    Abstract:

    We present the theory for a technique, based on multistate variants of the stimulated Raman adiabatic passage (STIRAP) process, that allows efficient and robust preparation of a preselected Superposition of two or three degenerate states (magnetic sublevels of an atom) and the measurement of their relative amplitudes and phases. Because the preparation utilizes adiabatic passage it is robust against small fluctuations of the Rabi frequencies and temporal shapes of the coupling fields. We here describe and, in the following companion paper we demonstrate, an approach to the experimental characterization of the Superposition state, i.e., the measurement of the relative phases and the ratios of amplitudes of the components. That technique, termed phase-to-population mapping, is applicable to the characterization of a stream of identically prepared atoms and is based on laser-induced fluorescence after the atoms have undergone optical pumping cycles induced by an additional laser. The optical pumping process maps the phase into populations of a subset of levels by means of a filtering laser field, and is robust against variations in the intensity and detuning of that field. We describe four linkage patterns appropriate to the creation of Superpositions of two or three degenerate states of angular momentum $J=2$, starting from $J=0$. We offer an interpretation, from three different perspectives, of the subsequent characterization procedure.

  • adiabatic creation of Coherent Superposition states in atomic beams
    Physical Review A, 2004
    Co-Authors: R G Unanyan, Monika E Pietrzyk, B W Shore, K Bergmann
    Abstract:

    We describe a technique for creating Superpositions of degenerate quantum states, such as are needed for beam splitters used in matter-wave optics, by manipulating the timing of three orthogonally polarized laser beams through which moving atoms (or molecules) pass; motion across the laser beams produces pulses in the atomic rest frame. As illustrated with representative simulations for transitions in metastable neon, a single pass through three overlapping laser beams can produce Superpositions (with preselected phase) of atomic beams differing by transverse momentum corresponding to the momentum of four photons. Like the two-photon momentum transfer of the tripod linkage pattern which it extends, the method relies on controlled adiabatic time evolution in the Hilbert subspace of two degenerate dark states. It is thus a generalization to multiple dark states (and larger transfers of linear momentum to the atomic beam) of the single dark state occurring with the stimulated Raman adiabatic passage (STIRAP) technique, and therefore it is potentially insensitive to decoherence due to spontaneous emission. By extending the tripod-linkage system to more numerous degenerate states, the technique not only increases the atomic beam deflections but, as we demonstrate, allows control over the Superposition phase and amplitudes. Like other techniques based on more » adiabatic time evolution, the technique is robust with respect to variations of the intensity, timing, and other characteristics of the laser fields. Unlike STIRAP, the same robust partial population transfer occurs for opposite timings of the pulse sequence, as is needed for such procedures as Hadamard gates. « less

  • creation and measurement of a Coherent Superposition of quantum states
    Physical Review Letters, 2003
    Co-Authors: Frank Vewinger, Manfred Heinz, Ruth Garcia Fernandez, Nikolay V Vitanov, K Bergmann
    Abstract:

    We demonstrate experimental techniques for creating and measuring a Coherent Superposition of two degenerate atomic states with equal amplitudes in metastable neon. Starting from state (3)P(0), we create adiabatically a Coherent Superposition of the magnetic sublevels M=+/-1 of the state (3)P(2) using a tripod stimulated Raman adiabatic passage scheme. The measurement is based on the coupling of the levels (3)P(2) (3)P(1) by a linearly polarized laser, followed by the detection of the population in the (3)P(2)(M=+/-2) states as a function of the polarization angle of that laser.

  • preparation of an n component maximal Coherent Superposition state using the stimulated raman adiabatic passage method
    Physical Review A, 2001
    Co-Authors: R G Unanyan, B W Shore, K Bergmann
    Abstract:

    We present a simple method for creating a maximal Coherent Superposition of N states (a Superposition state with equal amplitudes) in a robust way. We show that in the adiabatic limit the robustness of the population transfer out of a single state to the Superposition state is equivalent to stimulated Raman adiabatic passage. As is typical for schemes based upon population trapping the method is insensitive to radiative decay from excited states.

D F Coker - One of the best experts on this subject based on the ideXlab platform.

  • iterative linearized density matrix propagation for modeling Coherent excitation energy transfer in photosynthetic light harvesting
    Journal of Chemical Physics, 2010
    Co-Authors: Pengfei Huo, D F Coker
    Abstract:

    Rather than inCoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs Coherently, and involves Coherent Superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized Coherent Superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study Coherent excitation energy transfer in a model of the Fenna–Matthews–Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approxim...

  • iterative linearized density matrix propagation for modeling Coherent excitation energy transfer in photosynthetic light harvesting
    Journal of Chemical Physics, 2010
    Co-Authors: D F Coker
    Abstract:

    Rather than inCoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs Coherently, and involves Coherent Superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized Coherent Superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study Coherent excitation energy transfer in a model of the Fenna–Matthews–Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approximation to the density matrix propagator that accounts for interference between forward and backward paths of the quantum excitonic system while linearizing the phase in the difference between the forward and backward paths of the environmental degrees of freedom resulting in a classical-like treatment of these variables. The approach avoids making the Markovian approximation and we demonstrate that it successfully describes the Coherent beating of the site populations on different chromophores and gives good agreement with other methods that have been developed recently for going beyond the usual approximations, thus providing a new reliable theoretical tool to study Coherent exciton transfer in light harvesting systems. We conclude with a discussion of decoherence in independent bilinearly coupled harmonic chromophore baths. The ILDM propagation approach in principle can be applied to more general descriptions of the environment.Rather than inCoherent hopping between chromophores, experimental evidence suggests that the excitation energy transfer in some biological light harvesting systems initially occurs Coherently, and involves Coherent Superposition states in which excitation spreads over multiple chromophores separated by several nanometers. Treating such delocalized Coherent Superposition states in the presence of decoherence and dissipation arising from coupling to an environment is a significant challenge for conventional theoretical tools that either use a perturbative approach or make the Markovian approximation. In this paper, we extend the recently developed iterative linearized density matrix (ILDM) propagation scheme [E. R. Dunkel et al., J. Chem. Phys. 129, 114106 (2008)] to study Coherent excitation energy transfer in a model of the Fenna–Matthews–Olsen light harvesting complex from green sulfur bacteria. This approach is nonperturbative and uses a discrete path integral description employing a short time approxim...

Xingwen Yi - One of the best experts on this subject based on the ideXlab platform.

  • enhanced performance of phase conjugated ofdm subcarriers using digital Coherent Superposition
    Photonic Network Communications, 2016
    Co-Authors: Xingwen Yi, Changwei Tang, Hongyan Zhou, Dengke Zeng
    Abstract:

    We have recently demonstrated the improved phase noise tolerance in Coherent optical OFDM by digital Coherent Superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitian symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. According to the concept of phase-conjugated twin wave, both approaches can also mitigate the fiber nonlinearity to the first order. We prove that both approaches can cancel the inter-carrier interference (ICI) due to phase noise to the second order, and we derive the reduced ICI power to the fourth order using the Wiener phase noise model. In simulation, we show the enhanced tolerance to the laser phase noise and fiber nonlinearity.

  • Theoretical calculation on ICI reduction using digital Coherent Superposition of optical OFDM subcarrier pairs in the presence of laser phase noise
    Optics Express, 2014
    Co-Authors: Xingwen Yi, Bo Xu
    Abstract:

    Digital Coherent Superposition (DCS) of optical OFDM subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-OFDM that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to OFDM subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-OFDM is expected to be beneficial to certain optical fiber transmissions.

  • Digital Coherent Superposition of optical OFDM subcarrier pairs with Hermitian symmetry for phase noise mitigation
    Optics Express, 2014
    Co-Authors: Xingwen Yi, Xuemei Chen, Dinesh Sharma, Qi Yang, Chao Li, Zhaohui Li
    Abstract:

    Digital Coherent Superposition (DCS) provides an approach to combat fiber nonlinearities by trading off the spectrum efficiency. In analogy, we extend the concept of DCS to the optical OFDM subcarrier pairs with Hermitian symmetry to combat the linear and nonlinear phase noise. At the transmitter, we simply use a real-valued OFDM signal to drive a Mach-Zehnder (MZ) intensity modulator biased at the null point and the so-generated OFDM signal is Hermitian in the frequency domain. At receiver, after the conventional OFDM signal processing, we conduct DCS of the optical OFDM subcarrier pairs, which requires only conjugation and summation. We show that the inter-carrier-interference (ICI) due to phase noise can be reduced because of the Hermitain symmetry. In a simulation, this method improves the tolerance to the laser phase noise. In a nonlinear WDM transmission experiment, this method also achieves better performance under the influence of cross phase modulation (XPM).

  • Experimental Demonstration of Digital Coherent Superposition of Optical OFDM Subcarrier Pairs for Mitigation of Linear and Nonlinear Phase Noise
    Optical Fiber Communication Conference, 2014
    Co-Authors: Xingwen Yi, Xuemei Chen, Qi Yang, Chao Li, Zhaohui Li
    Abstract:

    We experimentally demonstrate digital Coherent Superposition of optical OFDM subcarrier pairs with Hermitian symmetry to mitigate phase noise, including laser phase noise and cross-phase modulation in a WDM transmission.

Andrew M Weine - One of the best experts on this subject based on the ideXlab platform.

  • 50 ghz spaced comb of high dimensional frequency bin entangled photons from an on chip silicon nitride microresonator
    Optics Express, 2018
    Co-Authors: Poolad Imany, Joseph M. Lukens, Pavel Lougovski, Ogaga D. Odele, Daniel E. Leaird, Jose A Jaramillovillegas, Andrew M Weine
    Abstract:

    Quantum frequency combs from chip-scale integrated sources are promising candidates for scalable and robust quantum information processing (QIP). However, to use these quantum combs for frequency domain QIP, demonstration of entanglement in the frequency basis, showing that the entangled photons are in a Coherent Superposition of multiple frequency bins, is required. We present a verification of qubit and qutrit frequency-bin entanglement using an on-chip quantum frequency comb with 40 mode pairs, through a two-photon interference measurement that is based on electro-optic phase modulation. Our demonstrations provide an important contribution in establishing integrated optical microresonators as a source for high-dimensional frequency-bin encoded quantum computing, as well as dense quantum key distribution.

Zhaohui Li - One of the best experts on this subject based on the ideXlab platform.