arXiv subjects

Chang Jian Kwong

Publications and source records attributed to Chang Jian Kwong.

5 recordsLinked to original sources

arXiv2025

Guidelines for designs for ultrastable laser with $\mathbf{10^{-17}}$ fractional frequency instability

Lasers with long coherence time and narrow linewidth are an essential tool for quantum sensors and clocks. Ultrastable cavities and laser systems are now commercially available with fractional frequency instabilities in the mid $10^{-16}$ range. This document aims to provide technical guidance for researchers starting in the field of ultrastable lasers and to give an outlook toward the next generation of improved ultrastable lasers. These guidelines have arisen from the scope of the EMPIR project ``Next generation ultrastable lasers'' ( https://www.ptb.de/empir2021/nextlasers ) with contributions from the European project partners.

physics.optics↗

arXiv2020

A simplified cryogenic optical resonator apparatus providing ultra-low frequency drift

A system providing an optical frequency with an instability comparable to that of a hydrogen maser is presented. It consists of a $5$ $\mathrm{cm}$ long, vertically oriented silicon optical resonator operated at temperatures between $1.5$ $\mathrm{K}$ and $3.6$ $\mathrm{K}$ in a closed-cycle cryostat with low-temperature Joule-Thomson stage. We show that with a standard cryostat, a simple cryogenic optomechanical setup, no active or passive vibration isolation, a minimum frequency instability of $2.5\times10^{-15}$ at $τ=1500$ $\mathrm{s}$ integration time can be reached. The influence of pulse-tube vibrations was minimized by using a resonator designed for low acceleration sensitivity. With reduced optical laser power and interrogation duty cycle an ultra-low fractional frequency drift of $-2.6\times10^{-19}$/$\mathrm{s}$ is reached. At $3.5$ $\mathrm{K}$ the resonator frequency exhibits a vanishing thermal sensitivity and an ultra-small temperature derivative $8.5\times10^{-12}/\mathrm{K}^{2}$. These are favorable properties that should lead to high performance also in simpler cryostats not equipped with a Joule-Thomson stage.

physics.ins-det↗

arXiv2018

Coherent transfer of singlet-triplet qubit states in an architecture of triple quantum dots

We propose two schemes to coherently transfer arbitrary quantum states of the two-electron singlet-triplet qubit across a chain of 3 quantum dots. The schemes are based on electrical control over the detuning energy of the quantum dots. The first is a pulse-gated scheme, requiring dc pulses and engineering of inter- and intra-dot Coulomb energies. The second scheme is based on the adiabatic theorem, requiring time-dependent control of the detuning energy through avoided crossings at a rate that the system remains in the ground state. We simulate the transfer fidelity using typical experimental parameters for silicon quantum dots. Our results give state transfer fidelities between $94.3\% < \mathcal{F} < 99.5\%$ at sub-ns gate times for the pulse-gated scheme and between $75.4\% < \mathcal{F} < 99.0 \%$ at tens of ns for the adiabatic scheme. Taking into account dephasing from charge noise, we obtain state transfer fidelities between $94.0\% < \mathcal{F} < 99.2\%$ for the pulse-gated scheme and between $64.9\% < \mathcal{F} < 93.6\%$ for the adiabatic scheme.

quant-ph↗

arXiv2018

Characterization of the long-term dimensional stability of a NEXCERA block using the optical resonator technique

NEXCERA is a machinable and highly polishable ceramic with attractive properties for use in precision instruments, in particular because its coefficient of thermal expansion exhibits a zero crossing at room temperature. We performed an accurate measurement of the long-term drift of the length of a 12~cm long NEXCERA block by using it as a spacer of a high-finesse optical cavity. At room temperature, we found a fractional length drift rate $L^{-1}dΔL/dt=-1.74\times10^{-8}~\mathrm{yr}^{-1}$.

physics.ins-det↗

arXiv2016

Entanglement Detection with Single Hong-Ou-Mandel Interferometry

Entanglement is not only fundamental for understanding multipartite quantum systems but also generally useful for quantum information applications. Despite much effort devoted so far, little is known about minimal resources for detecting entanglement and also comparisons to tomography which reveals the full characterization. Here, we show that all entangled states can in general be detected in an experimental scheme that estimates the fidelity of two pure quantum states. An experimental proposal is presented with a single Hong-Ou-Mandel interferometry in which only two detectors are applied regardless of the dimensions or the number of modes of quantum systems. This shows measurement settings for entanglement detection are in general inequivalent to tomography: the number of detectors in quantum tomography increases with the dimensions and the modes whereas it is not the case in estimation of fidelity which detects entangled states.

quant-ph↗