Time Gating Research Articles

Single-shot detection of bacterial spores with Yb-laser-based CARS spectroscopy.

We present a system based on a high-energy femtosecond ytterbium laser seeding an optical parametric amplifier and a photonic crystal hollow core fiber (PCHCF) compressor for coherent anti-Stokes Raman scattering (CARS) spectroscopy. The PCHCF provides spectral broadening of the Stokes pulse which is then compressed to a duration matched to that of the pump pulse. In these conditions, the excitation efficiency of vibrational levels in the target molecules is largely improved, as the time gating effect due to the mismatch between the durations of the pump and Stokes pulses is avoided. Experiments are presented along with a theoretical model to quantify expected improvement of sensitivity. The system is used to detect bacterial spores deposited on a surface with a single laser shot at unprecedented signal-to-noise ratio.

Speeding up qubit control with bipolar single-flux-quantum pulse sequences

The development of quantum computers based on superconductors requires the improvement of the qubit state control approach aimed at the increase of the hardware energy efficiency. A promising solution to this problem is the use of superconducting digital circuits operating with single-flux-quantum (SFQ) pulses, moving the qubit control system into the cold chamber. However, the qubit gate time under SFQ control is still longer than under conventional microwave driving. Here we introduce the bipolar SFQ pulse control based on ternary pulse sequences. We also develop a robust optimization algorithm for finding a sequence structure that minimizes the leakage of the transmon qubit state from the computational subspace. We show that the appropriate sequence can be found for arbitrary system parameters from the practical range. The proposed bipolar SFQ control reduces a single qubit gate time by halve compared to nowadays unipolar SFQ technique, while maintaining the gate fidelity over 99.99%.

Increasing the scan speed in high resolution, low energy electron diffraction measurements by presetting the gate time.

We report on a speed-up data acquisition routine for recording intensities in reciprocal space (k-space) with increased scan speed by a single point detector. It is designed for recording low energy electron diffraction (LEED) data with high resolution by a spot profile analysis LEED instrument. It counteracts the problem of long acquisition times that are encountered when larger areas in the reciprocal space are scanned. It exploits the fact that in typical LEED images of ordered surfaces, more than 90% of the data points in k-space belong to the low-intense background, which is often not of interest. Only about 10% of the data points are related to the relevant diffraction features, namely, the LEED spots. Often it is not necessary to measure the background with the same statistical significance as measuring those points that contain information. The data points belonging to the LEED spots can be discriminated from those of the background by their higher intensities. An acquisition routine that sets an increased gate time for the counting in response to higher intensities thus safeguards good statistics for data points of the LEED spots and saves measurement time when recording data points of the background with small gate times. For typical LEED images, a reduction of the total acquisition time by a factor of about 10 is obtained. We give examples of one- and two-dimensional scans from current experiments, recorded with and without the speed-up routine. We further discuss how the routine supports the measurement of energy dependent reciprocal space maps.

Robust two-qubit gates using pulsed dynamical decoupling

We present the experimental implementation of a two-qubit phase gate, using a radio frequency (RF) controlled trapped-ion quantum processor. The RF-driven gate is generated by a pulsed dynamical decoupling sequence applied to the ions’ carrier transitions only. It allows for a tunable phase shift with high-fidelity results. The conditional phase shift is measured using a Ramsey-type measurement with an inferred fringe contrast of up to . We also prepare a Bell state using this laser-free gate. The phase gate is robust against common sources of error. We investigate the effect of the excitation of the center-of-mass (COM) mode, errors in the axial trap frequency, pulse area errors and errors in sequence timing. The contrast of the phase gate is not significantly reduced up to a COM mode excitation 20 phonons, trap frequency errors of +10%, and pulse area errors of −8%. The phase shift is not significantly affected up to 10 phonons and pulse area errors of −2%. Both, contrast and phase shift are robust to timing errors up to −30% and +15%. The gate implementation is resource efficient, since only a single driving field is required per ion. Furthermore, it holds the potential for fast gate speeds (gate times on the order of 100 µs) by using two axial motional modes of a two-ion crystal through improved setups.

Low dose and low dose rate radioluminescence dosimetry

Review is provided of a number of low-dose, low dose rate situations that in study require advances in the development of dosimetric facilities. Using a clinical linac set up to provide doses down to the few mGy level, the performance of a real-time radioluminescence system has then been illustrated, accommodating pulsed as well as continuous dose delivery. The system gate times provide for tracking of the pattern of dose delivery, allowing detailed account of dose and dose-rate variations. The system has been tested in both x-ray and electron mode dose delivery.

High-speed feedback based wavefront shaping for spatiotemporal enhancement of incoherent light through dynamic scattering media.

Feedback-based wavefront shaping is a promising and versatile technique for enhancing the contrast of a target signal for both coherent and incoherent light through a highly scattering medium. However, this technique can fail for a dynamic sample with a short correlation time. So far, most proposed methods for high-speed wavefront shaping can only directly enhance the intensity of coherent light but not incoherent light. Here we try to fill this gap to directly enhance incoherent light with high speed, such as fluorescence, which is essential in extending wavefront shaping to biomedical applications. For this purpose, we develop a technique based on a single acousto-optic deflector (AOD) with field-programmable gate array (FPGA) acceleration for spatiotemporal focusing within milliseconds. With the digital time gating of the feedback signal, spatiotemporal focusing of laser light with high contrast can be formed behind dynamic scattering media in milliseconds resulting in fluorescence enhancement. Furthermore, FPGA-based wavefront shaping is shown to effectively enhance fluorescence directly behind dynamic samples with short correlation times.

Synthesis of and compilation with time-optimal multi-qubit gates

We develop a method to synthesize a class of entangling multi-qubit gates for a quantum computing platform with fixed Ising-type interaction with all-to-all connectivity. The only requirement on the flexibility of the interaction is that it can be switched on and off for individual qubits. Our method yields a time-optimal implementation of the multi-qubit gates. We numerically demonstrate that the total multi-qubit gate time scales approximately linear in the number of qubits. Using this gate synthesis as a subroutine, we provide compilation strategies for important use cases: (i) we show that any Clifford circuit on n qubits can be implemented using at most 2n multi-qubit gates without requiring ancilla qubits, (ii) we decompose the quantum Fourier transform in a similar fashion, (iii) we compile a simulation of molecular dynamics, and (iv) we propose a method for the compilation of diagonal unitaries with time-optimal multi-qubit gates, as a step towards general unitaries. As motivation, we provide a detailed discussion on a microwave controlled ion trap architecture with magnetic gradient induced coupling (MAGIC) for the generation of the Ising-type interactions.

Single-shot time-folded fluorescence lifetime imaging

Fluorescence lifetime imaging is an important tool in bioimaging that allows one to detect subtle changes in cell dynamics and their environment. Most time-domain approaches currently involve scanning a single illumination point across the sample, which can make imaging dynamic scenes challenging, while single-shot "rapid lifetime determination" can suffer from large uncertainties when the lifetime is not appropriately sampled. Here, we propose a time-folded fluorescence lifetime imaging microscopy (TFFLIM) approach, whereby a time-folding cavity provides multiple spatially sheared replicas of the lifetime, each shifted temporally with respect to a fixed time gate. This provides a robust, single-shot FLIM approach that we experimentally validate across a broad lifetime range on fluorescent beads and Convallaria samples.

Single-Flux-Quantum-Activated Controlled- Z Gate for Transmon Qubits

Single-flux-quantum (SFQ) digital circuitry has great potential in building a scalable control system of superconducting qubits. In this work, we describe a practical SFQ-based two-qubit gate for transmon qubits. The controlled-$Z$ (CZ) gate is activated by near-resonant SFQ-pulse trains near the target transition involving the second excited state. Numerical simulations show that the fidelity of a SFQ-activated CZ gate in excess of 99.9% is achievable within 100-ns gate time. We evaluate the CZ gate error caused by leakage and SFQ-pulse width. Combined with the proposed feasible expansion methods, this work is a supplement to the scalable and integratable superconducting-qubit control system based on SFQ digital logic.

Ultrasonic imaging of damage in plates in spectral ripple frequency domain

The ultrasonic C-scan method is a well-known non-destructive inspection method which typically analyzes ultrasound echoes in time domain. Although demonstrated for a variety of defects and materials, it has certain challenges in correctly assessing complex and distributed defects in multi-layer heterogeneous materials, e.g. barely visible impact damage in composite laminates.This paper proposes a C-scan imaging technique in the spectral ripple frequency domain by exploiting interference phenomena between multiple ultrasonic echoes in the response signal. The spectral ripple frequency domain imaging method processes the full A-scan signal without having to define an evaluation time gate. As such, it is highly suited for inspection of curved or tilted parts, or parts having different thickness sections. The method is demonstrated on several 5.5 mm thick carbon fiber reinforced polymer laminates with barely visible impact damage, revealing its capability to resolve neighboring delaminations and small defect fragments over the entire depth of the sample. The spectral ripple frequency domain imaging method shows good performance on datasets with high noise levels and/or low sampling rates, and is computationally very efficient, allowing real-time defect imaging.

Controlled-Controlled-Phase Gates for Superconducting Qubits Mediated by a Shared Tunable Coupler

Applications for noisy intermediate-scale quantum computing devices rely on the efficient entanglement of many qubits to reach a potential quantum advantage. Although entanglement is typically generated using two-qubit gates, direct control of strong multiqubit interactions can improve the efficiency of the process. Here, we investigate a system of three superconducting transmon-type qubits coupled via a single flux-tunable coupler. Tuning the frequency of the coupler by adiabatic flux pulses enables us to control the conditional energy shifts between the qubits and directly realize multiqubit interactions. To accurately adjust the resulting controlled relative phases, we describe a gate protocol involving refocusing pulses and adjustable interaction times. This enables the implementation of the full family of pairwise controlled-phase and controlled-controlled-phase gates. Numerical simulations result in fidelities around 99% and gate times below 300 ns using currently achievable system parameters and decoherence rates.

Stability of laser cavity-solitons for metrological applications

Laser cavity-solitons can appear in systems comprised of a nonlinear microcavity nested within an amplifying fiber loop. These states are robust and self-emergent and constitute an attractive class of solitons that are highly suitable for microcomb generation. Here, we present a detailed study of the free-running stability properties of the carrier frequency and repetition rate of single solitons, which are the most suitable states for developing robust ultrafast and high repetition rate comb sources. We achieve free-running fractional stability on both optical carrier and repetition rate (i.e., 48.9 GHz) frequencies on the order of 10−9 for a 1 s gate time. The repetition rate results compare well with the performance of state-of-the-art (externally driven) microcomb sources, and the carrier frequency stability is in the range of performance typical of modern free-running fiber lasers. Finally, we show that these quantities can be controlled by modulating the laser pump current and the cavity length, providing a path for active locking and long-term stabilization.

Shortcuts to adiabaticity in a fast controlled-phase gate in superconducting quantum circuits

Based on renewed interest in the shortcut-to-adiabaticity techniques in quantum control, we propose a reverse-engineering approach to modulate the longitudinal coupling between a pair of two-level systems with a quantized single-mode resonator. This allows us to suppress the unwanted transitions in the time-evolution operator such that the system dynamics resemble a controlled-phase gate acting in the qubit subspace at the nanosecond scale. The reduced gating time mitigates the detrimental effect produced by the loss mechanisms in all aspects. Moreover, we present a possible experimental implementation based on superconducting quantum circuits. Our work further demonstrates the versatility of the reverse-engineering method to enhance quantum protocols based on circuit quantum electrodynamic architecture.

Quantum control of tunable-coupling transmons using dynamical invariants of motion

We analyze the implementation of a fast nonadiabatic CZ gate between two transmon qubits with tunable coupling. The gate control method is based on a theory of dynamical invariants which leads to reduced leakage and robustness against decoherence. The gate is based on a description of the resonance between the and using an effective Hamiltonian with the six lowest energy states. A modification of the protocol allows us to take into account the higher-order perturbative corrections of this effective model. This enables a gate fidelity several orders of magnitude higher than other quasiadiabatic protocols, with gate times that approach the theoretical limit.

Realizing a class of stabilizer quantum error correction codes using a single ancilla and circular connectivity

We describe a class of "neighboring-blocks" stabilizer quantum error correction codes and demonstrate that such class of codes can be implemented in a resource-efficient manner using a single ancilla and circular near-neighbor qubit connectivity. We propose an implementation for syndrome-measurement circuits for codes from the class and illustrate its workings for cases of 3-qubit repetition code, Laflamme's 5-qubit code, and Shor's 9-qubit code. For 3-qubit repetition code and Laflamme's 5-qubit code suggested scheme has the property that it uses only native two-qubit CNS gates, which potentially reduces the amount of non-correctable errors due to the shorter gate time. Elements of the scheme can be used to implement surface code with near-neighbour connectivity using single ancilla, as demonstrated in an example. We developed efficient decoding procedures for repetition codes and the Laflamme's 5-qubit code using a minimum weight-perfect matching approach to account for the specific order of measurements in our scheme. The analysis of noise levels for which the scheme could show improvements in the fidelity of a stored logical qubit in the 3-qubit repetition code and Laflamme's 5-qubit code cases is provided. We complement our results by realizing the developed scheme for a 3-qubit code using an IBM quantum processor and the Laflamme's 5-qubit code using the state-vector simulator.

Acoustic cavitation localization during histotripsy using transmit-receive capable arrays

The nucleation and collapse of cavitation generated during histotripsy results in point-like emissions of shockwaves. Owing to the short duration acoustic pulses utilized during histotripsy the acoustic background from pulse reflections off intervening tissues is minimal and temporally isolated. This allows acoustic cavitation emission (ACE) shockwaves to be differentiated from the background in measured signals using simplified approaches such as peak detection and time gating, even in signals acquired using narrow bandwidth receivers such as the transmitting elements of the histotripsy array. The array elements allow acquisitions from across the array's entire aperture, which in turn allows cavitation to be localized in 3D. Here we describe multiple methods for localizing cavitation and evaluating induced tissue damage based on ACE signals measured using transmit-receive capable histotripsy arrays. The speed and accuracy of the methods were evaluated in ex vivo and in vitro experiments. Cavitation could be localized in 3D at rates >100Hz. Mean localization errors, with respect to measurements from optical images, were <2 mm (approximately the diameter of the generated bubbles). Cavitation lifespans could be assessed concurrently with the bubbles' 3D locations and correlated well with histological observations of induced damage, allowing 3D assessments of damage.

Fast parametric two-qubit gate for highly detuned fixed-frequency superconducting qubits using a double-transmon coupler

High-performance two-qubit gates have been reported with superconducting qubits coupled via a single-transmon coupler (STC). Most of them are implemented for qubits with a small detuning since reducing residual ZZ coupling for highly detuned qubits by an STC is challenging. In terms of the frequency crowding and crosstalk, however, highly detuned qubits are desirable. Here, we numerically demonstrate a high-performance parametric gate for highly detuned fixed-frequency qubits using a recently proposed tunable coupler called a double-transmon coupler (DTC). Applying an ac flux pulse, we can perform a maximally entangling universal gate (iSWAP) with an average fidelity over 99.99% and a short gate time of about 24 ns. This speed is comparable to resonance-based gates for slightly detuned tunable qubits. Moreover, using a dc flux pulse alternatively, we can achieve another kind of entangling gate called a CZ gate with an average fidelity over 99.99% and a gate time of about 18 ns. Given the flexibility and feasible settings, we can expect that the DTC will contribute towards realizing a high-performance quantum computer in the near future.

Straightforward bias- and frequency-dependent small-signal model extraction for single-layer graphene FETs

We propose an explicit small-signal graphene field-effect transistor (GFET) parameter extraction procedure based on a charge-based quasi-static model. The dependence of the small-signal parameters on both gate voltage and frequency is precisely validated by high-frequency (up to 18 GHz) on-wafer measurements from a 300 nm device. These parameters are studied simultaneously, in contrast to other works which focus exclusively on few. Efficient procedures have been applied to GFETs for the first time to remove contact and gate resistances from the Y-parameters. The use of these methods yields straightforward equations for extracting the small-signal model parameters, which is extremely useful for radio-frequency circuit design. Furthermore, we show for the first time experimental validation vs. both gate voltage and frequency of the intrinsic GFET non-reciprocal capacitance model. Accurate models are also presented for the gate voltage-dependence of the measured unity-gain and maximum oscillation frequencies as well as of the current and power gains.

On the Importance of Consistent Insonation Conditions During Hydrophone Calibration and Use.

Hydrophones are generally calibrated in acoustic fields with temporally localized (short pulse) or long duration (tone burst) signals. Free-field conditions are achieved by time gating any reflections from the hydrophone body, mounting structures, and surrounding water tank boundaries arriving at the active sensing element. Consequently, the sensitivity response of the hydrophone is a result of direct waves incident on its active element, free from any contaminating effects of reflections. However, when using tone bursts below 400 kHz to calibrate hydrophones, it may not be possible to isolate the direct wave from reflection artifacts. This means that the sensitivity responses derived at these frequencies using short pulse and tone burst signals might not be comparable as they can be characteristic of the acoustic field interaction with either/both the hydrophone active element alone or the hydrophone active element and body. Therefore, there is a need to consider an appropriate calibration method for a given hydrophone type, depending on whether the eventual application employs short pulse or tone burst acoustic fields. This article presents the findings from a short study comprising four needle-type hydrophones of active element diameters in the range of 1-4 mm. These hydrophones were calibrated from 30 kHz to 1.6 MHz using established calibration methodologies within the underwater acoustics (UWA) and ultrasound (US) areas employed at the National Physical Laboratory (NPL), Teddington, U.K. In UWA tone, burst acoustic fields are used, while in US, it is short pulses. The 2- and 4-mm-diameter needle hydrophones showed the largest variation at the overlapping frequencies, in which the maximum disagreement of UWA calibration was 30% relative to US calibration. For the 4-mm hydrophone, UWA calibration exhibited resonant sensitivity structure between 100 and 450 kHz, but which was absent in US calibration. This observed behavior was further investigated theoretically by using a validated acoustic wave solver to confirm the resonant sensitivity structure seen in the case of UWA calibration. The work contained within illustrates the need to ensure that the method of calibration is carefully considered in the context of the duration of the acoustic signals for which the hydrophone is intended.

Design of 15 level reduced switches inverter topology using multicarrier sinusoidal pulse width modulation

In this proposed paper, multicarrier sinusoidal pulse width modulation (M-SPWM) method is implemented for design of 15 level reduced switches inverter topology. This inverter topology generates 15 level output-voltage with suitablelswitching pulse production using M-SPWM and altered level of voltages are attained with distinction of modulationlindex. The split inductor is used to diminish the harmoniclcontent and flatted output current. This type of system which contains different range of different range of voltage supplies. As a result, this inverter reduces the difficulty in gating time calculation and there is no neutral point fluctuation issue. This paper illuminates the modes of switching and minimization of stress in voltage and harmonic diminution are examined. The grades of the projected multilevel inverter (MLI) system are verified using Matlab/Simulink and dsPIC controller respectively.