Amplifier Channels Research Articles

Quantum channels from reflections on moving mirrors

Light reflection on a mirror can be thought as a simple physical effect. However if this happens when the mirror moves a rich scenario opens up. Here we aim at analyzing it from a quantum communication perspective. In particular, we study the kind of quantum channel that arises from (Gaussian) light reflection upon an accelerating mirror. Two competing mechanisms emerge in such a context, namely photons production by the mirror’s motion and interference between modes. As consequence we find out a quantum amplifier channel and quantum lossy channel respectively below and above a threshold frequency (that depends on parameters determining mirror’s acceleration). Exactly at the threshold frequency the channel behaves like a purely classical additive channel, while it becomes purely erasure for large frequencies. In addition the time behavior of the channel is analyzed by employing wave packets expansion of the light field.

Repurchase Agreements and the European Sovereign Debt Crises: The Role of European Clearinghouses

This article investigates the European repo market and its role as an amplification channel for sovereign-debt crises. We focus on the centrally cleared segment, representing the majority of European repos. A novel data set on repo and margin haircuts applied to sovereign bonds by central clearing counter parties (CCPs) is gathered, allowing us to assess the haircut methodologies used by the major European CCPs. We document that following increases in sovereign risk, haircuts set bymajor CCPs on peripheral sovereign bonds increased significantly. The procyclicality of haircuts and the concentration of bilateral repos raise concerns about the CCP-intermediated repo market as a source of systemic risk in the Eurozone. This is however mitigated by the counter cyclical monetary policy of the European Central Bank (ECB).

Aggregating quantum repeaters for the quantum internet

The quantum internet holds promise for accomplishing quantum teleportation and unconditionally secure communication freely between arbitrary clients all over the globe, as well as the simulation of quantum many-body systems. For such a quantum internet protocol, a general fundamental upper bound on the obtainable entanglement or secret key has been derived [K. Azuma, A. Mizutani, and H.-K. Lo, Nat. Commun. 7, 13523 (2016)]. Here we consider its converse problem. In particular, we present a universal protocol constructible from any given quantum network, which is based on running quantum repeater schemes in parallel over the network. For arbitrary lossy optical channel networks, our protocol has no scaling gap with the upper bound, even based on existing quantum repeater schemes. In an asymptotic limit, our protocol works as an optimal entanglement or secret-key distribution over any quantum network composed of practical channels such as erasure channels, dephasing channels, bosonic quantum amplifier channels, and lossy optical channels.

Scaling maps of s -ordered quasiprobabilities are either nonpositive or completely positive

Continuous-variable systems in quantum theory can be fully described through any one of the $s$-ordered family of quasiprobabilities ${\mathrm{\ensuremath{\Lambda}}}_{s}(\ensuremath{\alpha}), s\ensuremath{\in}[\ensuremath{-}1,1]$. We ask for what values of $(s,a)$ is the scaling map ${\mathrm{\ensuremath{\Lambda}}}_{s}(\ensuremath{\alpha})\ensuremath{\rightarrow}{a}^{\ensuremath{-}2}{\mathrm{\ensuremath{\Lambda}}}_{s}({a}^{\ensuremath{-}1}\ensuremath{\alpha})$ a positive map? Our analysis based on a duality we establish settles this issue: (i) the scaling map generically fails to be positive, showing that there is no useful entanglement witness of the scaling type beyond the transpose map, and (ii) in the two particular cases $(s=1,|a|\ensuremath{\le}1)$ and $(s=\ensuremath{-}1,|a|\ensuremath{\ge}1)$, and only in these two nontrivial cases, the map is not only positive but also completely positive as seen through the noiseless attenuator and amplifier channels. We also present a ``phase diagram'' for the behavior of the scaling maps in the $s\ensuremath{-}a$ parameter space with regard to its positivity, obtained from the viewpoint of symmetric-ordered characteristic functions. This also sheds light on similar diagrams for the practically relevant attenuation and amplification maps with respect to the noise parameter, especially in the range below the complete-positivity (or quantum-limited) threshold.

A rocket Langmuir sonde for measurements of the plasma characteristics in the lower ionosphere

The design of a rocket Langmuir sonde is described. The electrical circuits of the EU are presented and their specific features are considered. Laboratory investigations of the EU were performed. The nonlinearity of each of six channels of amplifiers–converters does not exceed 1%. The range of the sonde-recorded signals is 30 pA–5 μA; the nonlinearity (as a function of time) of the generator-formed potential at the measuring electrode is 1% or less. Bench tests were performed that confirmed the serviceability of the sonde under the conditions of mechanical and thermal loads that occur during a rocket flight. The technical possibilities of the sonde make it possible to monitor the charged component in the lower ionosphere (100–300 km) from a meteorological rocket; in this case, the density variations of the flows of free electrons and positive ions to the measuring electrode relative to their average value may amount to 2 orders of magnitude. In comparison to its analogues, the sonde provides a higher sensitivity of measurements and a higher time resolution and distorts the electric field in the vicinity of the measuring electrode to a lower degree. The electron-energy distribution function can be reconstructed from the current–voltage characteristic up to the energies of epithermal electrons.

Possible acceleration of cosmic rays in a system of rotating gases: Uehling–Uhlenbeck model

Possible acceleration of cosmic rays passing through a kind of amplification channel (via anomalous diffusion modes of propagating plane-wave fronts) induced by a system of rotating gases (or disk-like gases) is presented. Our novel numerical results after detailed analysis were based on the quantum discrete kinetic model (considering Uehling–Uhlenbeck collision term) which has been used to study the propagation of plane (e.g., acoustic) waves propagating in composite-particle gases under uniform gravitational fields.

A fast, low power and low noise charge sensitive amplifier ASIC for a UV imaging single photon detector

NASA has funded, through their Strategic Astrophysics Technology (SAT) program, the development of a cross strip (XS) microchannel plate (MCP) detector with the intention to increase its technology readiness level (TRL), enabling prototyping for future NASA missions. One aspect of the development is to convert the large and high powered laboratory Parallel Cross Strip (PXS) readout electronics into application specific integrated circuits (ASICs) to decrease their mass, volume, and power consumption (all limited resources in space) and to make them more robust to the environments of rocket launch and space. The redesign also foresees to increase the overall readout event rate, and decrease the noise contribution of the readout system. This work presents the design and verification of the first stage for the new readout system, the 16 channel charge sensitive amplifier ASIC, called the CSAv3. The single channel amplifier is composed of a charge sensitive amplifier (pre-amplifier), a pole zero cancellation circuit and a shaping amplifier. An additional output stage buffer allows polarity selection of the output analog signal. The operation of the amplifier is programmable via serial bus. It provides an equivalent noise charge (ENC) of around 600 e^− and a baseline gain of 10 mV/fC. The full scale pulse shaped output signal is confined within 100 ns, without long recovery tails, enabling up to 10 MHz periodic event rates without signal pile up. This ASIC was designed and fabricated in 130 nm, TSMC CMOS 1.2 V technology. In addition, we briefly discuss the construction of the readout system and plans for the future work.

A Wide Dynamic Range CMOS Laser Radar Receiver With a Time-Domain Walk Error Compensation Scheme

This integrated receiver channel designed for a pulsed time-of-flight (TOF) laser rangefinder consists of a fully differential transimpedance amplifier channel and a timing discriminator. The amplitude-dependent timing walk error is compensated by measuring the width and rise time of the received pulse echo and using this information for calibration. The measured bandwidth, transimpedance and minimum detectable signal (SNR ~10) of the receiver channel are 230 MHz, $100~\text {k}\Omega $ and ${\sim } 1~\mu \text {A}$ respectively. The single-shot precision of the receiver is ~3 cm at an SNR of 13 and the measurement accuracy is ±4 mm with compensation within a dynamic range of ~1:100 000. The receiver circuit was realized in a $0.35~\mu \text {m}$ CMOS process and has a power consumption of 150 mW. The functionality of the receiver channel was verified over a temperature range of -20 °C to +50 °C.

The Anatomy of Financial Vulnerabilities and Crises

We extend the framework used in Aikman, Kiley, Lee, Palumbo, and Warusawitharana (2015) that maps vulnerabilities in the U.S. financial system to a broader set of advanced and emerging economies. Our extension tracks a broader set of vulnerabilities and, therefore, captures signs of different types of crises. The typical anatomy of the evolution of vulnerabilities before and after a financial crisis is as follows. Pressures in asset valuations materialize, and a build-up of imbalances in the external, financial, and nonfinancial sectors follows. A financial crisis is typically followed by a build-up of sovereign debt imbalances as the government tries to deal with the consequences of the crisis. Our early warnings indicators which aggregate these vulnerabilities predict banking crises better than the Credit-to-GDP gap at long horizons. Our indicators also predict the severity of banking crises and the duration of recessions, as they take into account possible spill-over and amplification channels of financial stress to from one to another sector in the economy. Our indicators are of relevance for macroprudential and crisis management, in part, because they perform better than the Credit-to-GDP gap and do not suffer from the gaps econometric flaws.

Capacities of quantum amplifier channels

Quantum amplifier channels are at the core of several physical processes. Not only do they model the optical process of spontaneous parametric down-conversion, but the transformation corresponding to an amplifier channel also describes the physics of the dynamical Casimir effect in superconducting circuits, the Unruh effect, and Hawking radiation. Here we study the communication capabilities of quantum amplifier channels. Invoking a recently established minimum output-entropy theorem for single-mode phase-insensitive Gaussian channels, we determine capacities of quantum-limited amplifier channels in three different scenarios. First, we establish the capacities of quantum-limited amplifier channels for one of the most general communication tasks, characterized by the trade-off between classical communication, quantum communication, and entanglement generation or consumption. Second, we establish capacities of quantum-limited amplifier channels for the trade-off between public classical communication, private classical communication, and secret key generation. Third, we determine the capacity region for a broadcast channel induced by the quantum-limited amplifier channel, and we also show that a fully quantum strategy outperforms those achieved by classical coherent detection strategies. In all three scenarios, we find that the capacities significantly outperform communication rates achieved with a naive time-sharing strategy.

Universal self-amplification channel for surface plasma waves

We present a theory of surface plasma waves (SPWs) in metals with arbitrary electronic collision rate ${\ensuremath{\tau}}^{\ensuremath{-}1}$. We show that there exists a universal intrinsic amplification channel for these waves, subsequent to the interplay between ballistic motions and the metal surface. We evaluate the corresponding amplification rate ${\ensuremath{\gamma}}_{0}$, which turns out to be a sizable fraction of the SPW frequency ${\ensuremath{\omega}}_{s}$. We also find that the value of ${\ensuremath{\omega}}_{s}$ depends on surface scattering properties, in contrast with the conventional theory.

Effects of nonlinear amplification on differential sensitivity measures in individuals with cochlear hearing impairment

Objective: The current study focused on exploring the influence of multichannel amplification with wide dynamic range compression (WDRC) on frequency, intensity, and duration discrimination measures at two frequencies in different channels of amplification. Methods: Discrimination measures were performed on twenty ears with moderate flat sensorineural hearing loss using 2-down and 1-up adaptive procedure to achieve 70.7% response on the psychometric function. All stimuli were generated through AUX script and presented using Psycon version 2.18 experimental software and delivered through the speakers oriented at an angle of 0° azimuth. Discrimination measures were performed in both aided and unaided conditions for two pure tone frequencies of 750 and 1500 Hz with 500 ms duration (on/off ramp duration of 80 ms to avoid spectral splatter) presented at a level of 20 dBSL (with reference to the threshold separately in each condition). The responses were recorded through three interval alternative forced choice paradigm with visual feedback. An average of final four reversals out of eight was considered for discrimination threshold estimation. Results and Conclusions: Results revealed a statistically significant deterioration in intensity discrimination and a significant improvement in difference limen for frequency and duration with nonlinear amplification. The deteriorated intensity discrimination scores were explained in perspectives of WDRC acting in amplification device.

Possible acceleration of cosmic rays in a rotating system: Uehling-Uhlenbeck model

We illustrate the possible acceleration of cosmic rays passing through a kind of amplification channel (via diffusion modes of propagating plane-wave fronts) induced by a rotating system. Our analysis is mainly based on the quantum discrete kinetic model (considering a discrete Uehling-Uhlenbeck collision term), which has been used to study the propagation of plane (e.g., acoustic) waves in a system of rotating gases.

Institutional Herding and Its Price Impact: Evidence from the Corporate Bond Market

Among growing concerns about potential financial stability risks posed by the asset management industry, herding has been considered as an important risk amplification channel. In this paper, we examine the extent to which institutional investors herd in their trading of U.S. corporate bonds and quantify the price impact of such herding behavior. We find that, relative to what is documented for the equity market, the level of institutional herding is much higher in the corporate bond market, particularly among speculative-grade bonds. In addition, mutual funds have become increasingly likely to herd when they sell, a trend not observed among insurance companies and pension funds. We also show that bond investors herd not only within a quarter, but also over adjacent quarters. Such persistence in trading is largely driven by funds imitating the trading behavior of other funds in the previous quarter. Finally, we find that there is an asymmetry in the price impact of herding. While buy herding is associated with a permanent price impact that is consistent with price discovery, sell herding results in transitory yet significant price distortions. The price destabilizing effect of sell herding is particularly strong for high-yield bonds, small bonds, and illiquid bonds and during the recent global financial crisis.

The acoustical performance of an ultrasound matrix transducer directly stacked on a silicon chip

Clinical studies have shown a high demand for 3D real time ultrasound imaging for accurate diagnosis. One way to scan a volume with high frame rate is to design a 2D matrix transducer allowing beamforming in both lateral and elevation directions. Recent developments in manufacturing technologies allow the integration of a matrix of piezoelectric elements on Application Specific Integrated Circuit (ASIC). The ASIC is responsible for beamforming, amplification, switching, and significant channel count reduction. Traditionally, the backing material for a linear/phased array is composed of a mixture of epoxy with powder of heavy materials, which causes strong attenuation. This avoids energy being reflected back into to the elements and results in short pulses, high bandwidth, and consequently high axial resolution of the image. However, the ASIC acoustically behaves like a hard and non-absorbing backing material. Therefore, the acoustical energy of the piezoelectric pillar propagates into the chip and affects the performance of the neighbouring elements. In this paper we numerically investigate the effect of the ASIC on the acoustical performance of a transducer. In particular, the transmit and receive performance, crosstalk, and directivity pattern are compared with the results for a traditional backing material.

Uncertainty shocks, banking frictions and economic activity

In this paper we investigate the effects of uncertainty shocks on economic activity in the euro area by using a Dynamic Stochastic General Equilibrium (DSGE) model with heterogenous agents and a stylized banking sector. We show that frictions in credit supply amplify the effects of uncertainty shocks on economic activity. This amplification channel stems mainly from the stickiness in bank loan rates. This stickiness reduces the effectiveness in the transmission mechanism of monetary policy.

Multi-kilowatt diffractive coherent combining of pseudorandom-modulated fiber amplifiers

We report efficient coherent beam combining of five kW-class fiber amplifiers seeded with pseudorandom phase-modulated light, using a 1×5 diffractive optical element (DOE). Each fiber amplifier channel was path length matched, actively polarized, and provided approximately 1.2 kW of near diffraction-limited output power (M2<1.1). A low-power sample of the combined beam after the DOE provided an error signal for active phase stabilization. After phase stabilization, the beams were coherently combined via the DOE. Notably, a total output power of ∼5 kW was achieved with 82% combining efficiency and excellent beam quality (M2<1.1). The intrinsic DOE splitter loss was 5%. Additional losses due in part to nonideal polarization, amplified spontaneous emission content, uncorrelated wavefront errors, and fractional beam misalignments contributed to the efficiency reduction. Overall, multi-kW beam combining of pseudorandom-modulated fiber amplifiers was demonstrated for the first time.

A brief assessment of Turkey's macroprudential policy approach: 2011–2015

The predominant role of cross border financial flows for macroeconomic and financial stability has imposed complex policy trade-offs for emerging economies, especially after the global financial crisis. This note provides a brief account of the macroprudential policy approach adopted in Turkey between the years 2011 and 2015, a period when global capital flows exhibited unprecedented volatility. Special emphasis is put on the use of monetary policy tools for macroprudential purposes. We first highlight the particular role of external flows and the associated tradeoffs in designing the monetary policy and macroprudential policy framework. Next, we describe the policy implementation by the central bank and the regulatory authorities, and evaluate the consequent outcomes. Our analysis suggests that macroprudential policies have improved external balances, dampened financial amplification channels, and reduced the sensitivity of the Turkish economy to capital flows.

1kW 1mJ eight-channel ultrafast fiber laser.

An ultrafast fiber chirped-pulse amplifier comprising eight coherently combined amplifier channels is presented. The laser delivers 1kW average power at 1mJ pulse energy and 260fs pulse duration. Excellent beam quality and low-noise performance are confirmed. The laser has proven suitable for demanding scientific applications. Further power scaling is possible right away using even more amplifier channels.

12 mJ kW-class ultrafast fiber laser system using multidimensional coherent pulse addition.

An ultrafast fiber-chirped-pulse amplification system using a combination of spatial and temporal coherent pulse combination is presented. By distributing the amplification among eight amplifier channels and four pulse replicas, up to 12 mJ pulse energy with 700 W average power and 262 fs pulse duration have been obtained with a system efficiency of 78% and excellent beam quality. To the best of our knowledge, this is the highest energy achieved by an ultrafast fiber-based laser system to date.