Sub-picosecond Precision Research Articles

Enhancing quantum time transfer security: detecting intercept-resend attacks with energy-time entanglement

Abstract Quantum time transfer has emerged as a powerful technique, offering sub-picosecond precision and inherent security through the nonlocal temporal correlation property of energy-time entangled biphoton sources. In this paper, we demonstrate the inherent security advantage of quantum time transfer, and the utilization in detecting potential intercept-resend attacks. By investigating the impact of these attacks on the nonlocality identifier associated with nonlocal dispersion cancellation of energy-time entanglement, we establish a security threshold model for detecting intercept-resend attacks. Experimental verification on a 102 km fiber-optic link confirms that even a malicious delay as small as 25 ps can be identified. This investigation serves as a compelling illustration of secure two-way time transfer, safeguarding against intercept-resend attacks, and showcasing its potential applications in fields reliant on authentic time distribution between remote parties.

Large dynamic range digital delay with sub-picosecond precision

We report on the development and performance of a digitally controlled phase delay with a step of 280 femtoseconds and a dynamic range of 230 picoseconds. Details of the device design and the simulations as well as comparisons with laboratory measurements will be discussed. We describe how we have used this ASIC to stabilize a digital clock to a precision of less than one picosecond.

Optical Imaging of Ultrafast Phonon-Polariton Propagation through an Excitonic Sensor.

Hexagonal boron nitride (hBN) hosts phonon polaritons (PhP), hybrid light-matter states that facilitate electromagnetic field confinement and exhibit long-range ballistic transport. Extracting the spatiotemporal dynamics of PhPs usually requires "tour de force" experimental methods such as ultrafast near-field infrared microscopy. Here, we leverage the remarkable environmental sensitivity of excitons in two-dimensional transition metal dichalcogenides to image PhP propagation in adjacent hBN slabs. Using ultrafast optical microscopy on monolayer WSe2/hBN heterostructures, we image propagating PhPs from 3.5 K to room temperature with subpicosecond and few-nanometer precision. Excitons in WSe2 act as transducers between visible light pulses and infrared PhPs, enabling visible-light imaging of PhP transport with far-field microscopy. We also report evidence of excitons in WSe2 copropagating with hBN PhPs over several micrometers. Our results provide new avenues for imaging polar excitations over a large frequency range with extreme spatiotemporal precision and new mechanisms to realize ballistic exciton transport at room temperature.

A high precision phase measurement system implemented in FPGA with phase interpolator.

High precision timing distribution is crucial to many large scale cosmology and particle physics experiments. Besides the space and energy information, the accurate timing provides an extra dimension for physics event reconstruction. In the timing distribution system, accurate clock phase measurement is an indispensable tool to monitor the phase drift and to achieve accurate phase adjustment. This paper introduces a novel phase measurement method implemented in the Xilinx Field Programmable Gate Array (FPGA). It uses the dedicated phase interpolator in the multi-gigabit transceiver. A design based on this method is implemented within the Kintex Ultrascale series FPGA. The preliminary test result shows that a sub-picosecond level precision is achieved. With this system, the nonlinearity of the phase adjustment in the Xilinx transceiver is measured.

Fiber-optic two-way quantum time transfer with frequency-entangled pulses

High-precision time transfer is of fundamental interest in physics and metrology. Quantum time transfer technologies that use frequency-entangled pulses and their coincidence detection have been proposed, offering potential enhancements in precision and better guarantees of security. In this paper, we describe a fiber-optic two-way quantum time transfer experiment. Using quantum nonlocal dispersion cancellation, time transfer over a 20-km fiber link achieves a time deviation of 922 fs over 5 s and 45 fs over 40960 s. The time transfer accuracy as a function of fiber lengths from 15 m to 20 km is also investigated, and an uncertainty of 2.46 ps in standard deviation is observed. In comparison with its classical counterparts, the fiber-optic two-way quantum time transfer setup shows appreciable improvement, and further enhancements could be obtained by using new event timers with sub-picosecond precision and single-photon detectors with lower timing jitter for optimized coincidence detection. Combined with its security advantages, the femtosecond-scale two-way quantum time transfer is expected to have numerous applications in high-precision middle-haul synchronization systems.

Note: Low phase noise programmable phase-locked loop with high temperature stability.

The design and construction of low jitter programmable phase-locked loop with low temperature coefficient of phase are presented. It has been designed for demanding high precision timing applications, especially as a clock source for event timer with subpicosecond precision. The phase-locked loop itself has a jitter of few hundreds of femtoseconds. It produces square wave with programmable output frequency from 100 MHz to 500 MHz and programmable amplitude of 0.25 V to 1.2 V peak-to-peak, which is locked to 5 MHz or 10 MHz reference frequency common for disciplined oscillators and highly stable clocks such as hydrogen maser. Moreover, it comprises an on-board temperature compensated crystal oscillator for stand-alone usage. The device provides temperature coefficient of the phase lock of 0.9 ps/K near room temperature.

Two-way time transfer via optical fiber providing subpicosecond precision and high temperature stability

We are reporting on analysis, design, construction, and key parameters of the device for a two-way time transfer via an optical fiber. The dominant source of errors in the two-way optical time transfer (TWOTT) via relatively short optical fibers is the temperature dependence of internal delays within the terminal units. We have performed an analysis of the influence of the internal delays and their temperature dependence on the TWOTT process considering two different configurations of the terminals with the feedback coupling in optical and electrical domains. The achieved results have been used for the optimal design of a TWOTT system implementing standard small form-factor pluggable optical transceivers. The operational tests of this new TWOTT system confirmed the precision of the time transfer on the subpicosecond level, the time transfer stability characterized by TDEV better than 60 fs for averaging intervals from 100 s to 10 000 s, and the temperature stability better than 100 fs K−1.

Frequency-domain acquisition of fourth-order correlation by spectral intensity interferometry

We report on the spectral intensity interferometer (SII) which is a frequency-domain variant of the fourth-order interferometry. In the SII, the power spectrum of the intensity is acquired for light fields of an interferometer. It produces a fringed spectral interferogram which can be acquired by means of an electric spectrum analyzer in keeping the relative time delay constant during the acquisition. Through both theoretical and experimental investigations, we have found that the SII interferogram provides the intensity correlation information without concern of field-sensitive disturbances which are vulnerable to minute variations of the optical paths. As an application example, a precision time-of-flight measurement was demonstrated by using a fiber-optic SII with an amplified spontaneous emission (ASE) light source. A large delay of 4.1-km long fiber was successfully analyzed from the fringe period. Its wavelength-dependent group delay or the group velocity dispersion (GVD) was also measured from the phase shift of the cosine fringe with a sub-picosecond delay precision.

Note: Electronic circuit for two-way time transfer via a single coaxial cable with picosecond accuracy and precision

We have designed, constructed, and tested the overall performance of the electronic circuit for the two-way time transfer between two timing devices over modest distances with sub-picosecond precision and a systematic error of a few picoseconds. The concept of the electronic circuit enables to carry out time tagging of pulses of interest in parallel to the comparison of the time scales of these timing devices. The key timing parameters of the circuit are: temperature change of the delay is below 100 fs/K, timing stability time deviation better than 8 fs for averaging time from minutes to hours, sub-picosecond time transfer precision, and a few picoseconds time transfer accuracy.

A 10-GHz global clock distribution using coupled standing-wave oscillators

In this paper, a global clock network that incorporates standing waves and coupled oscillators to distribute a high-frequency clock signal with low skew and low jitter is described. The key design issues involved in generating standing waves on a chip are discussed, including minimizing wire loss within an available technology. A standing-wave oscillator, which is a distributed oscillator that sustains ideal standing waves on lossy wires, is introduced. A clock grid architecture comprised of coupled standing-wave oscillators and differential low-swing clock buffers is presented, along with a compact circuit model for networks of oscillators. The measured results for a prototyped standing-wave clock grid operating at 10 GHz and fabricated in a 0.18-/spl mu/m 6M CMOS logic process are presented. A technique is proposed for on-chip skew measurements with subpicosecond precision.

Subpicosecond laser ablation of dental enamel

Laser ablation of dental enamel with subpicosecond laser pulses has been studied over the intensity range of (0.1–1.4)×1014 W/cm2 using 95 and 150 fs pulses at a pulse repetition rate of 1 kHz. The experimentally determined ablation threshold of 2.2±0.1 J/cm2 was in good agreement with theoretical predictions based on an electrostatic ablation model. The ablation rate increased linearly with the laser fluence for up to 15 times the ablation threshold. The absence of collateral damage was observed using optical and scanning electron microscopy. Pulpal temperature measurements showed an increase of about 10 °C during the 200 s course of ablation. However, air cooling at a rate of 5 l/min resulted in the intrapulpal temperature being maintained below the pulpal damage threshhold of 5.5 °C. The material removal rates for subpicosecond precision laser ablation of dental enamel are compared with other techniques.

The measurements of picosecond fluorescence lifetimes with high accuracy and subpicosecond precision

Systematic studies of the fluorescence picosecond lifetimes determination by laser-excited time-correlated single-photon-counting (TCSPC) have been undertaken. The results have been used to develop methods for determining lifetimes with much smaller error and much greater reproducibility than any hitherto reported. The error in the determination of the lifetimes (±three standard deviations) can be as low as that in simulations and amounts to 0.01 FWHM of the IRF. The lifetimes determined for the second excited singlet state of xanthione in toluene (5.1±0.3 ps) and in benzene (8.1±0.3 ps) can be treated as reliable standards of picosecond lifetimes.

Picosecond photoluminescence nonlinearity of two-dimensional plasma in GaAs-(Al 0.3Ga 0.7As) multiple quantum wells

CW and sub-picosecond excitation correlation photoluminescence techniques were utilized to characterize the 2D-plasma modulation doped in the GaAs-Al 0.3Ga 0.7As multiple quantum wells. The gain or loss of photoluminescence intensity was found to be closely related to the excitation intensity. In addition, the relaxation time as a function of excitation intensity was determined with sub-picosecond precision, and theoretically can be attributable to phonon reabsorption.

On-chip picosecond time-domain measurements for VLSI and interconnect testing using photoconductors

Picosecond time-domain measurements of silicon IC interconnects were successfully performed using photoconductors integrated on-chip. Standard IC fabrication techniques followed by shadow-masked ion-beam irradiation were used to create the photoconductor/interconnect structures. Starting materials used were 70-Ω.cm n-type wafers and 16-Ω. cm p-type wafers. A subpicosecond pulsed laser system excited the photoconductors to produce and sample picosecond pulses on the Si substrate. These integrated photoconductors can also be used to perform picosecond transient measurements of VLSI devices and circuits. Optoelectronic cross-correlation measurements with photoconductor pulsers and photoconductor sampling gates were performed to characterize both the on-chip photoconductors and the on-chip interconnects. Photoconductors processed as pulsers produced electrical pulses with ∼ 2-ps rise time, ∼ 200-mV peak amplitude and full width at half-maximum (FWHM) of < 10 ps. Photoconductors processed as sampling gates demonstrated 3-dB measurement bandwidths of 20 GHz. Due to the absence of jitter on-chip signal delays were measured with subpicosecond precision.

On-Chip Picosecond Time-Domain Measurements for VLSI and Interconnect Testing Using Photoconductors

Picosecond time-domain measurements of silicon IC interconnects were successfully performed using photoconductors integrated on-chip. Standard IC fabrication techniques followed by shadow-masked ion-beam irradiation were used to create the photoconductor/interconnect structures. Starting materials used were 70-/spl Omega//spl dot/cm n-type wafers and 16-/spl Omega//spl dot/cm p-type wafers. A subpicosecond pulsed laser system excited the photo-conductors to produce and sample picosecond pulses on the Si substrate. These integrated photoconductors can also be used to perform picosecond transient measurements of VLSI devices and circuits. Optoelectronic cross-correlation measurements with photoconductor pulsers and photoconductor sampling gates were performed to characterize both the on-chip photoconductors and the on-chip interconnects. Photoconductors processed as pulsers produced electrical pulses with ~ 2-ps rise time, ~ 200-mV peak amplitude and full width at half-maximum (FWHM) of < 10 ps. Photoconductors processed as sampling gates demonstrated 3-dB measurement bandwidths of 20 GHz. Due to the absence of jitter on-chip signal delays were measured with subpicosecond precision.

Integrated silicon photoconductors for picosecond pulsing and gating

Integrated photoconductors were constructed on a crystalline Si substrate through standard integrated circuit fabrication techniques followed by shadow-masked ion-beam irradiation. Optoelectronic cross-correlation measurements were performed on these structures with a femtosecond colliding-pulse mode-locked dye laser system. Photoconductors processed as pulsers produced <2-ps rise time ∼ 200-mV pulses with full width at half maxima (FWHM) of 20 ps. Photoconductors processed as sampling gates demonstrated 3-dB measurement bandwidths between 5.3 and 7.6 GHz. Due to the absence of jitter, on-chip signal delays were measured with sub-picosecond precision.