26 research outputs found
Experimental techniques for continuous variable photonic quantum information
No full textQuantum optics is central to emerging quantum technologies such as quantum metrology and quantum information. The continuous variable (CV) approach to encoding information in a physical system, for example the electromagnetic field quadratures has significant advantages over discrete variables (DV) encoding. CV offers higher density encoding in a single optical state and on-demand state preparation for example. However, techniques for CV preparation, manipulation and measurement are not as well developed as the corresponding DV approach. In this thesis we present methods to characterize quantum detectors that operate in the CV regime, and discuss their application to CV state preparation. A quantum detector is described by its positive operator valued measure (POVM) set, with one operator for each measurement outcome. We present an experimental scheme for detector tomography, that is reconstruction of the POVM set of an unknown detector by means of measurement outcomes for a set of tomographically complete input states. We use this scheme to experimentally determine the POVM set of an avalanche photodiode (APD) and a time-multiplexed-detector (TMD) and compare the results to models of the detectors. We introduce a weak-homodyne photon-number-resolving detector (PNRD) , which uses a weak local oscillator beam to set a phase reference for the detection process. We develop a theoretical description of the sensitivity regimes for this detector using the Wigner phase space picture. We also present experimental detector tomography for a weak-homodyne detector based on two APDs. In many cases it is sufficient to calibrate the efficiencies of previously characterized PNRDs. We experimentally demonstrate a scheme using correlated photons produced by spontaneous parametric downconversion (SPDC) to determine the efficiencies of PNRDs, based on the photon number statistics of the source. The same SPDC source is also used to demonstrate preparation of photonic states in the photon number basis and for a first proof-of-principle experiment with a weak-homodyne PNRD based on a TMD.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Quantum detector tomography of a time-multiplexed superconducting nanowire single-photon detector at telecom wavelengths
Get PDFSuperconducting nanowire single-photon detectors (SNSPDs) are widely used in telecom wavelength optical quantum information science applications. Quantum detector tomography allows the positive-operator-valued measure (POVM) of a single-photon detector to be determined. We use an all-fiber telecom wavelength detector tomography test bed to measure detector characteristics with respect to photon flux and polarization, and hence determine the POVM. We study the SNSPD both as a binary detector and in an 8-bin, fiber based, Time-Multiplexed (TM) configuration at repetition rates up to 4 MHz. The corresponding POVMs provide an accurate picture of the photon number resolving capability of the TM-SNSPD
Bridging Particle and Wave Sensitivity in a Configurable Detector of Positive Operator-Valued Measures
No full textPeer reviewed: YesNRC publication: Ye
Glacial-to-deglaical changes in South Pacific surface water oceanography - centennial-scale age control -
No full textGlacial-to-interglacial changes in atmospheric pCO2 are considered as largely controlled by processes in the Southern Ocean. In particular, upwelling both near coastlines and along the Polar Front is regarded as a major pathway of old CO2 from the deep ocean up to the sea surface and atmosphere, hence plays an important role in regulating the CO2 exchange between ocean and atmosphere. At the beginning of the last glacial termination, changes in ocean overturning circulation in the Southern Ocean probably triggered two huge events of CO2 outgassing from a deep-ocean reservoir into the atmosphere as revealed by Antarctic ice core records 1. They parallel two intervals of rapidly decreasing atmospheric 13C 2 and ∆14C 3. They probably concurred with two intervals of enhanced ocean upwelling, directly linking increased ventilation of the deep ocean to the deglacial rise in atmospheric CO2. To constrain the precise timing and origin of released CO2 we used paired records of marine 14C reservoir ages from the Pacific sector of the Southern Ocean, established by means of the 14C Plateau Tuning method 4. High surface ocean reservoir ages serve as tracer for upwelled old water masses. They were obtained from our centennial-scale resolution planktonic radiocarbon records of sediment cores off southern New Zealand and southern Chile. During the last peak glacial our 14C ages reveal planktonic reservoir ages of 1600 - 2200 yr exceeding previous estimates 5,6 by 400-1200 yr, but well agree to the previously reported high value of 1970 yr 7. Right at the onset of the last deglacial our records suggest an extreme drop down to a very low reservoir age of 200-400 yr matching the low estimates of 300-400 yr by 5,6,7,8. During terminal Heinrich-1 times, the values once more reached 1100 yr. This pattern of increased reservoir ages during peak glacial times (and the B/A) and strongly reduced values during the early deglacial parallels and precedes the 13C trends of atmospheric CO2 each and may have great implications for both constraining the history of past deep-water ages and related changes in the CO2 (1‰ 14C -1.22 μmol DIC kg−1) 4 storage of South Pacific deep waters.
(1) Marcott et al. 2014, Nature Vol. 514, 616
(2) Schmitt et al. 2013, Science Vol. 336, 711
(3) Bronk Ramsey et al. 2012, Science Vol. 338, 370
(4) Sarnthein et al. 2013, Clim. Past Vol. 9, 2595
(5) Pahnke et al. 2005, Science Vol. 307, 1741
(6) Ronge et al. 2016, Nature Comm. Vol. 7, 11487
(7) Sikes et al. 2000, Nature Vol. 405, 555
(8) Siani et al. 2013, Nature Comm. Vol. 4. 275
Photon number statistics of multimode parametric down-conversion.
No full textWe experimentally analyze the complete photon number statistics of parametric down-conversion and ascertain the influence of multimode effects. Our results clearly reveal a difference between single-mode theoretical description and the measured distributions. Further investigations assure the applicability of loss-tolerant photon number reconstruction and prove strict photon number correlation between signal and idler modes
Continuous phase stabilization and active interferometer control using two modes
No full textWe present a computer-based active interferometer stabilization method that can be set to an arbitrary phase difference and does not rely on modulation of the interfering beams. The scheme utilizes two orthogonal modes propagating through the interferometer with a constant phase difference between them to extract a common relative phase and generate a linear feedback signal. Switching times of 50ms over a range of 0-6π radians at 632.8 nm are experimentally demonstrated. The relative interferometer phase can be stabilized up to several days to within ± 3°. © 2011 Copyright Taylor and Francis Group, LLC
Recursive quantum detector tomography
Get PDFConventional tomographic techniques are becoming increasingly infeasible for reconstructing the operators of quantum devices of growing sophistication. We describe a novel tomographic procedure using coherent states, which begins by reconstructing the diagonals of the operator and then each successive off-diagonal in a recursive manner. Each recursion is considerably more efficient than reconstructing the operator in its entirety, and each successive recursion involves fewer parameters. We apply our technique to reconstruct the positive-operator-valued measure corresponding to a recently developed coherent optical detector with phase sensitivity and number resolution. We discuss the effect of various parameters on the reconstruction accuracy. The results show the efficiency of the method and its robustness to experimental noise. © IOP Publishing and Deutsche Physikalische Gesellschaft
Measuring measurement: theory and practice
Get PDFRecent efforts have applied quantum tomography techniques to the calibration and characterization of complex quantum detectors using minimal assumptions. In this work, we provide detail and insight concerning the formalism, the experimental and theoretical challenges and the scope of these tomographical tools. Our focus is on the detection of photons with avalanche photodiodes and photon-number resolving detectors and our approach is to fully characterize the quantum operators describing these detectors with a minimal set of well-specified assumptions. The formalism is completely general and can be applied to a wide range of detectors
Complete Characterization of Weak-Homodyne Photon-Number-Resolving Detectors: Applications to Non-Classical Photonic State Reconstructions
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