15 research outputs found
Foreign Exchange Market Microstructure and the WM/Reuters 4pm Fix
A market fix serves as a benchmark for foreign exchange (FX) execution, and
is employed by many institutional investors to establish an exact reference at
which execution takes place. The currently most popular FX fix is the World
Market Reuters (WM/R) 4pm fix. Execution at the WM/R 4pm fix is a service
offered by FX brokers (normally banks), who deliver execution at the fix
provided they obtain the trade order until a certain time prior to 4pm. In this
paper, we study the market microstructure around 4pm. We demonstrate that
market dynamics can be distinguished from other times during the day through
increased volatility and size of movements. Our findings question the aggregate
benefit to the client base of using the 4pm fix in its current form.Comment: 20 Pages, 6 Figures, 3 Table
Room temperature caesium quantum memory for quantum information applications
Quantum memories are key components in quantum information networks. Their
ability to store and retrieve information on demand makes repeat-until-success
strategies scalable. Warm alkali-metal vapours are interesting candidates for
the implementation of such memories, thanks to their long storage times and
experimental simplicity. Operation with the Raman protocol enables high
time-bandwidth products, which allows for multiple synchronisation trials of
probabilistically operating quantum gates via memory-based temporal
multiplexing. This makes the Raman memory a promising tool, whose broad
spectral bandwidth facilitates direct interfacing with other photonic
primitives, such as single photon sources. Here, such a light-matter interface
is implemented in a warm caesium vapour. Firstly, we study the storage of
polarisation-encoded information in the memory. High quality polarisation
preservation for bright coherent state input signals can be achieved, when
operating the Raman memory in a dual-rail configuration inside a polarisation
interferometer. Secondly, heralded single photons are stored in the memory. To
this end, the memory is operated on-demand by feed-forward of source heralding
events, which is a key technological capability. Prior to storage, single
photons are produced in a spontaneous parametric down conversion source, whose
bespoke design spectrally tailors the photons to the memory acceptance line.
The faithful retrieval of stored single photons is found to be currently
limited by noise in the memory, with a signal-to-noise ratio of 0.3 in the
memory output. Nevertheless, a clear influence of the input's quantum nature is
observed in the retrieved light by measuring signal's photon statistics.
Finally, the memory noise processes are examined in detail. Four-wave-mixing
noise is determined as the sole important noise source for the Raman memory
Practical methods for witnessing genuine multi-qubit entanglement in the vicinity of symmetric states
We present general numerical methods to construct witness operators for
entanglement detection and estimation of the fidelity. Our methods are applied
to detecting entanglement in the vicinity of a six-qubit Dicke state with three
excitations and also to further entangled symmetric states. All our witnesses
are designed to keep the measurement effort small. We present also general
results on the efficient local decomposition of permutationally invariant
operators, which makes it possible to measure projectors to symmetric states
efficientlyComment: 13 pages including 4 figures, revtex
Experimental entanglement of a six-photon symmetric Dicke state
We report on the experimental observation and characterization of a
six-photon entangled Dicke state. We obtain a fidelity as high as
0.6540.024 and prove genuine six-photon entanglement by, amongst others, a
two-setting witness yielding -0.4220.148. This state has remarkable
properties; e.g., it allows obtaining inequivalent entangled states of a lower
qubit number via projective measurements, and it possesses a high entanglement
persistency against qubit loss. We characterize the properties of the
six-photon Dicke state experimentally by detecting and analyzing the
entanglement of a variety of multipartite entangled states.Comment: replaced with published versio
Room temperature caesium quantum memory for quantum information applications
Quantum memories are key components in photonics-based quantum information processing networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their very long storage times as well as their experimental simplicity and versatility. Operation with the Raman memory protocol enables high time-bandwidth products, which denote the number of possible storage trials within the memory lifetime. Since large time-bandwidth products enable multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing, the Raman memory is a promising tool for such tasks. Particularly, the broad spectral bandwidth allows for direct and technologically simple interfacing with other photonic primitives, such as heralded single photon sources. Here, this kind of light-matter interface is implemented using a warm caesium vapour Raman memory. Firstly, we study the storage of polarisation-encoded quantum information, a common standard in quantum information processing. High quality polarisation preservation for bright coherent state input signals can be achieved, when operating the Raman memory in a dual-rail configuration inside a polarisation interferometer. Secondly, heralded single photons are stored in the memory. To this end, the memory is operated on-demand by feed-forward of source heralding events, which constitutes a key technological capability for applications in temporal multiplexing. Prior to storage, single photons are produced in a waveguide-based spontaneous parametric down conversion source, whose bespoke design spectrally tailors the heralded photons to the memory acceptance bandwidth. The faithful retrieval of stored single photons is found to be currently limited by noise in the memory, with a signal-to-noise ratio of approximately 0.3 in the memory output. Nevertheless, a clear influence of the quantum nature of an input photon is observed in the retrieved light by measuring the read-out signal's photon statistics via the g(2)-autocorrelation function. Here, we find a drop in g(2) by more than three standard deviations, from g(2) ∼ 1.69 to g(2) ∼ 1.59 upon changing the input signal from coherent states to heralded single photons. Finally, the memory noise processes and their scalings with the experimental parameters are examined in detail. Four-wave-mixing noise is determined as the sole important noise source for the Raman memory. These experimental results and their theoretical description point towards practical solutions for noise-free operation.</p
Room temperature caesium quantum memory for quantum information applications: Single photon raman quantum memory in room-temperature atomic caesium vapour
Quantum memories are key components in photonics-based quantum information processing networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their very long storage times as well as their experimental simplicity and versatility. Operation with the Raman memory protocol enables high time-bandwidth products, which denote the number of possible storage trials within the memory lifetime. Since large time-bandwidth products enable multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing, the Raman memory is a promising tool for such tasks. Particularly, the broad spectral bandwidth allows for direct and technologically simple interfacing with other photonic primitives, such as heralded single photon sources. Here, this kind of light-matter interface is implemented using a warm caesium vapour Raman memory. Firstly, we study the storage of polarisation-encoded quantum information, a common standard in quantum information processing. High quality polarisation preservation for bright coherent state input signals can be achieved, when operating the Raman memory in a dual-rail configuration inside a polarisation interferometer. Secondly, heralded single photons are stored in the memory. To this end, the memory is operated on-demand by feed-forward of source heralding events, which constitutes a key technological capability for applications in temporal multiplexing. Prior to storage, single photons are produced in a waveguide-based spontaneous parametric down conversion source, whose bespoke design spectrally tailors the heralded photons to the memory acceptance bandwidth. The faithful retrieval of stored single photons is found to be currently limited by noise in the memory, with a signal-to-noise ratio of approximately 0.3 in the memory output. Nevertheless, a clear influence of the quantum nature of an input photon is observed in the retrieved light by measuring the read-out signal's photon statistics via the g(2)-autocorrelation function. Here, we find a drop in g(2) by more than three standard deviations, from g(2) ∼ 1.69 to g(2) ∼ 1.59 upon changing the input signal from coherent states to heralded single photons. Finally, the memory noise processes and their scalings with the experimental parameters are examined in detail. Four-wave-mixing noise is determined as the sole important noise source for the Raman memory. These experimental results and their theoretical description point towards practical solutions for noise-free operation