27 research outputs found
Quantum optical non-linearities induced by Rydberg-Rydberg interactions: a perturbative approach
In this article, we theoretically study the quantum statistical properties of
the light transmitted through or reflected from an optical cavity, filled by an
atomic medium with strong optical non-linearity induced by Rydberg-Rydberg van
der Waals interactions. Atoms are driven on a two-photon transition from their
ground state to a Rydberg level via an intermediate state by the combination of
a weak signal field and a strong control beam. By using a perturbative
approach, we get analytic results which remain valid in the regime of weak
feeding fields, even when the intermediate state becomes resonant. Therefore
they allow us to investigate quantitatively new features associated with the
resonant behaviour of the system. We also propose an effective non-linear
three-boson model of the system which, in addition to leading to the same
analytic results as the original problem, sheds light on the physical processes
at work in the system
Instability to a heterogeneous oscillatory state in randomly connected recurrent networks with delayed interactions
Oscillatory dynamics are ubiquitous in biological networks. Possible sources of oscillations are well understood in low-dimensional systems but have not been fully explored in high-dimensional networks. Here we study large networks consisting of randomly coupled rate units. We identify a type of bifurcation in which a continuous part of the eigenvalue spectrum of the linear stability matrix crosses the instability line at nonzero frequency. This bifurcation occurs when the interactions are delayed and partially antisymmetric and leads to a heterogeneous oscillatory state in which oscillations are apparent in the activity of individual units but not on the population-average level
Versatile Wideband Balanced Detector for Quantum Optical Homodyne Tomography
We present a comprehensive theory and an easy to follow method for the design
and construction of a wideband homodyne detector for time-domain quantum
measurements. We show how one can evaluate the performance of a detector in a
specific time-domain experiment based on electronic spectral characteristic of
that detector. We then present and characterize a high-performance detector
constructed using inexpensive, commercially available components such as
low-noise high-speed operational amplifiers and high-bandwidth photodiodes. Our
detector shows linear behavior up to a level of over 13 dB clearance between
shot noise and electronic noise, in the range from DC to 100 MHz. The detector
can be used for measuring quantum optical field quadratures both in the
continuous-wave and pulsed regimes with pulse repetition rates up to about 250
MHz.Comment: 11 pages, 8 figures, 1 tabl
A search algorithm for quantum state engineering and metrology
In this paper we present a search algorithm that finds useful optical quantum states which can be created with current technology. We apply the algorithm to the field of quantum metrology with the goal of finding states that can measure a phase shift to a high precision. Our algorithm efficiently produces a number of novel solutions: we find experimentally-ready schemes to produce states that show significant improvements over the state-of-the-art, and can measure with a precision that beats the shot noise limit by over a factor of 4. Furthermore, these states demonstrate a robustness to moderate/high photon losses, and we present a conceptually simple measurement scheme that saturates the Cramer-Rao bound
Mapping coherence in measurement via full quantum tomography of a hybrid optical detector
Quantum states and measurements exhibit wave-like --- continuous, or
particle-like --- discrete, character. Hybrid discrete-continuous photonic
systems are key to investigating fundamental quantum phenomena, generating
superpositions of macroscopic states, and form essential resources for
quantum-enhanced applications, e.g. entanglement distillation and quantum
computation, as well as highly efficient optical telecommunications. Realizing
the full potential of these hybrid systems requires quantum-optical
measurements sensitive to complementary observables such as field quadrature
amplitude and photon number. However, a thorough understanding of the practical
performance of an optical detector interpolating between these two regions is
absent. Here, we report the implementation of full quantum detector tomography,
enabling the characterization of the simultaneous wave and photon-number
sensitivities of quantum-optical detectors. This yields the largest
parametrization to-date in quantum tomography experiments, requiring the
development of novel theoretical tools. Our results reveal the role of
coherence in quantum measurements and demonstrate the tunability of hybrid
quantum-optical detectors.Comment: 7 pages, 3 figure
Quantum-optical state engineering up to the two-photon level
The ability to prepare arbitrary quantum states within a certain Hilbert space is the holy grail of quantum information technology. It is particularly important for light, as this is the only physical system that can communicate quantum information over long distances. We propose and experimentally verify a scheme to produce arbitrary single-mode states of a travelling light field up to the two-photon level. The desired state is remotely prepared in the signal channel of spontaneous parametric down-conversion by means of conditional measurements on the idler channel. The measurement consists of bringing the idler field into interference with two ancilla coherent states, followed by two single-photon detectors, which, in coincidence, herald the preparation event. By varying the amplitudes and phases of the ancillae, we can prepare any arbitrary superposition of zero-, one- and two-photon states
Electromagnetically induced absorption in a nondegenerate three-level ladder system
We investigate, theoretically and experimentally, the transmission of light through a thermal vapor of three-level ladder-type atoms, in the presence of two counterpropagating control fields. A simple theoretical model predicts the presence of electromagnetically induced absorption in this pure three-level system when the control field is resonant. Experimentally, we use Rb87Rb87 in a large magnetic field of 0.62 T to reach the hyperfine Paschen–Back regime and realize a nondegenerate three-level system. Experimental observations verify the predictions over a wide range of detunings