Optimal Population Coding, Revisited

Cortical circuits perform the computations underlying rapid perceptual decisions within a few dozen milliseconds with each neuron emitting only a few spikes. Under these conditions, the theoretical analysis of neural population codes is challenging, as the most commonly used theoretical tool – Fisher information – can lead to erroneous conclusions about the optimality of different coding schemes. Here we revisit the effect of tuning function width and correlation structure on neural population codes based on ideal observer analysis in both a discrimination and reconstruction task. We show that the optimal tuning function width and the optimal correlation structure in both paradigms strongly depend on the available decoding time in a very similar way. In contrast, population codes optimized for Fisher information do not depend on decoding time and are severely suboptimal when only few spikes are available. In addition, we use the neurometric functions of the ideal observer in the classification task to investigate the differential coding properties of these Fisher-optimal codes for fine and coarse discrimination. We find that the discrimination error for these codes does not decrease to zero with increasing population size, even in simple coarse discrimination tasks. Our results suggest that quite different population codes may be optimal for rapid decoding in cortical computations than those inferred from the optimization of Fisher information

Overcoming Noise in Entanglement Distribution

Noise can be considered the natural enemy of quantum information. An often implied benefit of high-dimensional entanglement is its increased resilience to noise. However, manifesting this potential in an experimentally meaningful fashion is challenging and has never been done before. In infinite dimensional spaces, discretisation is inevitable and renders the effective dimension of quantum states a tunable parameter. Owing to advances in experimental techniques and theoretical tools, we demonstrate an increased resistance to noise by identifying two pathways to exploit high-dimensional entangled states. Our study is based on two separate experiments utilising canonical spatio-temporal properties of entangled photon pairs. Following these different pathways to noise resilience, we are able to certify entanglement in the photonic orbital-angular-momentum and energy-time degrees of freedom up to noise conditions corresponding to a noise fraction of 72 % and 92 % respectively. Our work paves the way towards practical quantum communication systems that are able to surpass current noise and distance limitations, while not compromising on potential device-independence.Comment: 12 pages main text, 7 pages supplementary information, 6 figure

Symbolic QED Pre-silicon Verification for Automotive Microcontroller Cores: Industrial Case Study

We present an industrial case study that demonstrates the practicality and effectiveness of Symbolic Quick Error Detection (Symbolic QED) in detecting logic design flaws (logic bugs) during pre-silicon verification. Our study focuses on several microcontroller core designs (~1,800 flip-flops, ~70,000 logic gates) that have been extensively verified using an industrial verification flow and used for various commercial automotive products. The results of our study are as follows: 1. Symbolic QED detected all logic bugs in the designs that were detected by the industrial verification flow (which includes various flavors of simulation-based verification and formal verification). 2. Symbolic QED detected additional logic bugs that were not recorded as detected by the industrial verification flow. (These additional bugs were also perhaps detected by the industrial verification flow.) 3. Symbolic QED enables significant design productivity improvements: (a) 8X improved (i.e., reduced) verification effort for a new design (8 person-weeks for Symbolic QED vs. 17 person-months using the industrial verification flow). (b) 60X improved verification effort for subsequent designs (2 person-days for Symbolic QED vs. 4-7 person-months using the industrial verification flow). (c) Quick bug detection (runtime of 20 seconds or less), together with short counterexamples (10 or fewer instructions) for quick debug, using Symbolic QED

Temporal distinguishability in Hong-Ou-Mandel interference: Generation and characterization of high-dimensional frequency entanglement

High-dimensional quantum entanglement is currently one of the most prolific fields in quantum information processing due to its high information capacity and error resilience. A versatile method for harnessing high-dimensional entanglement has long been hailed as an absolute necessity in the exploration of quantum science and technologies. Here we exploit Hong-Ou-Mandel interference to manipulate discrete frequency entanglement in arbitrary-dimensional Hilbert space. The generation and characterization of two-, four- and six-dimensional frequency entangled qudits are theoretically and experimentally investigated, allowing for the estimation of entanglement dimensionality in the whole state space. Additionally, our strategy can be generalized to engineer higher-dimensional entanglement in other photonic degrees of freedom. Our results may provide a more comprehensive understanding of frequency shaping and interference phenomena, and pave the way to more complex high-dimensional quantum information processing protocols

Optimisation of the Read-out Electronics of Muon Drift-Tube Chambers for Very High Background Rates at HL-LHC and Future Colliders

In the ATLAS Muon Spectrometer, Monitored Drift Tube (MDT) chambers and sMDT chambers with half of the tube diameter of the MDTs are used for precision muon track reconstruction. The sMDT chambers are designed for operation at high counting rates due to neutron and gamma background irradiation expected for the HL-LHC and future hadron colliders. The existing MDT read-out electronics uses bipolar signal shaping which causes an undershoot of opposite polarity and same charge after a signal pulse. At high counting rates and short electronics dead time used for the sMDTs, signal pulses pile up on the undershoot of preceding background pulses leading to a reduction of the signal amplitude and a jitter in the drift time measurement and, therefore, to a degradation of drift tube efficiency and spatial resolution. In order to further increase the rate capability of sMDT tubes, baseline restoration can be used in the read-out electronics to suppress the pile-up effects. A discrete bipolar shaping circuit with baseline restoration has been developed and used for reading out sMDT tubes under irradiation with a 24 MBq 90Sr source. The measurements results show a substantial improvement of the performance of the sMDT tubes at high counting rates

Polarization entanglement by time-reversed Hong-Ou-Mandel interference

Sources of entanglement are an enabling resource in quantum technology, and pushing the limits of generation rate and quality of entanglement is a necessary pre-requisite towards practical applications. Here, we present an ultra-bright source of polarization-entangled photon pairs based on time-reversed Hong-Ou-Mandel interference. By superimposing four pair-creation possibilities on a polarization beam splitter, pairs of identical photons are separated into two spatial modes without the usual requirement for wavelength distinguishability or non-collinear emission angles. Our source yields high-fidelity polarization entanglement and high pair-generation rates without any requirement for active interferometric stabilization, which makes it an ideal candidate for a variety of applications, in particular those requiring indistinguishable photons

Numerical Investigation of the Effects of Post-Combustion due to Fuel Outflow in Bleed Engine Cycles of a Retro Propulsion-Assisted Launch Vehicle

Reusable launch vehicles (RLV) have the potential to be a resource- and cost-efficient alternative to conventional space transport systems. Several first stages of RLVs are in the maturing process and the European long term strategy aims towards the development and characterization of RLV relevant technologies for their next generation of launchers. We are basing our studies on the EU funded Retro Propulsion Assisted Landing Technologies (RETALT) project, which was formed with the goal of investigating Vertical Take-off Vertical Landing (VTVL) launch vehicles. In this paper, the first stage of the VTVL Two Stage to Orbit (TSTO) RETALT1 configuration will be used for the assessment of thermal loads during the flight trajectory. The mission plan for the first stage of the RETALT1-vehicle is to return either to the launch pad or a drone ship via a re-entry burn and a retro propulsion maneuver. During this retro propulsion phase high thermal loads are acting on the rocket structure and especially the landing legs, the base plate and the aerodynamic control surfaces. These thermal loads due to the main engine exhaust of the RLV have been characterized in previous studies by Laureti et al. Only little research has been devoted to the topic of post combustion due to the outflow of gas generators and air vents of cryogenic fuel tanks in VTVL-configurations in general. Owing to these secondary exhaust jets, unburned hydrogen is ejected near the high temperature outflow of the main engines, which could lead to a significant post combustion with the surrounding atmospheric oxygen and deviating thermal loads along the vital parts of the rocket structure. In order to provide an assessment of the additional influence of the post combustion and thermal loads, Computational Fluid Dynamics (CFD) simulations are carried out using the DLR-TAU code with the Reynolds Averaged Navier Stokes (RANS) method. As the post-combustion of the nozzle- and gasgenerator-outflow is to be observed, a reduced Jachimowsky mechanism for a species mixture of the liquid hydrogen, liquid oxygen combustion mixture and ambient air is applied as chemistry model. In this publication the validity of the computational mesh by means of a GCI-study and the influence of the turbulence modeling with different approaches is to be investigated. With these results first observations of the flow field characteristics and the thermal loads acting on the RLV will be done in order to identify the simulation parameters, including crucial points along the flight trajectory for investigations of the heat flux distribution across the surface structures of the vehicle

Distribution of genuine high-dimensional entanglement over 10.2 km of noisy metropolitan atmosphere

In a recent quantum key distribution experiment, high-dimensional protocols were used to show an improved noise resistance over a 10.2 km free-space channel. One of the unresolved questions in this context is whether the communicating parties actually shared genuine high-dimensional entanglement. In this letter we introduce an improved discretisation and entanglement certification scheme for high-dimensional time-bin setups and apply it to the data obtained during the experiment. Our analysis answers the aforementioned question affirmatively and thus the experiment constitutes the first transmission of genuine high-dimensional entanglement in a single degree of freedom over a long-range free-space channel.Comment: 6 pages, 3 figure