arXiv subjects

Hao-Ze Chen

Publications and source records attributed to Hao-Ze Chen.

11 recordsLinked to original sources

arXiv2024

Microsatellite-based real-time quantum key distribution

A quantum network provides an infrastructure connecting quantum devices with revolutionary computing, sensing, and communication capabilities. As the best-known application of a quantum network, quantum key distribution (QKD) shares secure keys guaranteed by the laws of quantum mechanics. A quantum satellite constellation offers a solution to facilitate the quantum network on a global scale. The Micius satellite has verified the feasibility of satellite quantum communications, however, scaling up quantum satellite constellations is challenging, requiring small lightweight satellites, portable ground stations and real-time secure key exchange. Here we tackle these challenges and report the development of a quantum microsatellite capable of performing space-to-ground QKD using portable ground stations. The quantum microsatellite features a payload weighing approximately 23 kg, while the portable ground station weighs about 100 kg. These weights represent reductions by more than an order and two orders of magnitude, respectively, compared to the Micius satellite. Additionally, we multiplex bidirectional satellite-ground optical communication with quantum communication, enabling key distillation and secure communication in real-time. Using the microsatellite and the portable ground stations, we demonstrate satellite-based QKD with multiple ground stations and achieve the sharing of up to 0.59 million bits of secure keys during a single satellite pass. The compact quantum payload can be readily assembled on existing space stations or small satellites, paving the way for a satellite-constellation-based quantum and classical network for widespread real-life applications.

quant-ph↗

arXiv2021

Observation of the density dependence of the closed-channel fraction of a $^6$Li superfluid

Atomic Fermi gases provide an ideal platform for studying the pairing and superfluid physics, using a Feshbach resonance between closed channel molecular states and open channel scattering states. Of particular interest is the strongly interacting regime. We show that the closed-channel fraction $Z_{cc}$ provides an effective probe for the important many-body interacting effects, especially through its density dependence, which is absent from two-body theoretical predictions. Here we measure $Z_{cc}$ as a function of interaction strength and the Fermi temperature $T_\text{F}$ in a trapped $^6$Li superfluid throughout the entire BCS--BEC crossover, in quantitative agreement with theory when important thermal contributions outside the superfluid core are taken into account. Away from the deep BEC regime, the fraction $Z_{cc}$ is sensitive to $T_\text{F}$. In particular, our data show $Z_{cc} \propto T_\text{F}^α$ with $α=1/2$ at unitarity, in quantitative agreement with calculations of a two-channel pairing fluctuation theory, and $α$ increases rapidly into the BCS regime, reflecting many-body interaction effects as predicted.

cond-mat.quant-gas↗

arXiv2020

A 30 W, sub-kHz frequency-locked laser at 532 nm

We report on the realization of a high-power, ultranarrow-linewidth, and frequency-locked 532~nm laser system. The laser system consists of single-pass and intra-cavity second harmonic generation of a continuous-wave Ytterbium doped fiber laser at 1064~nm in the nonlinear crystal of periodically poled lithium niobate and lithium triborate, respectively. With 47~W infrared input, 30~W green laser is generated through the type I critical phase matching in the intracavity lithium triborate crystal. The laser linewidth is measured to be on the order of sub-kHz, which is achieved by simultaneously locking the single-pass frequency doubling output onto the iodine absorption line R69 (36-1) at 532~nm. Furthermore, the phase locking between the laser system and another slave 1064~nm laser is demonstrated with relative frequency tunability being up to 10~GHz. Our results completely satisfy the requirements of 532~nm laser for quantum simulation with ultracold atoms.

physics.optics↗

arXiv2020

Oscillatory-like Expansion of a Fermionic Superfluid

We study the expansion behaviours of a Fermionic superfluid in a cigar-shaped optical dipole trap for the whole BEC-BCS crossover and various temperatures. At low temperature ($0.06(1) T_F$), the atom cloud undergoes an anisotropic hydrodynamic expansion over 30~ms, which behaves like oscillation in the horizontal plane. By analyzing the expansion dynamics according to the superfluid hydrodynamic equation, the effective polytropic index $\barγ$ of Equation-of-State of Fermionic superfluid is extracted. The $\barγ$ values show a non-monotonic behavior over the BEC-BCS crossover, and have a good agreement with the theoretical results in the unitarity and BEC side. The normalized quasi-frequencies of the oscillatory expansion are measured, which drop significantly from the BEC side to the BCS side and reach a minimum value of 1.73 around $1/k_Fa=-0.25$. Our work improves the understanding of the dynamic properties of strongly interacting Fermi gas.

cond-mat.quant-gas↗

arXiv2017

Strongly Interacting Bose Gases near a $d$-wave Shape Resonance

Many unconventional quantum matters, such as fractional quantum Hall effect and $d$-wave high-Tc superconductor, are discovered in strongly interacting systems. Understanding quantum many-body systems with strong interaction and the unconventional phases therein is one of the most challenging problems in physics nowadays. Cold atom systems possess a natural way to create strong interaction by bringing the system to the vicinity of a scattering resonance. Although this has been a focused topic in cold atom physics for more than a decade, these studies have so far mostly been limited for $s$-wave resonance. Here we report the experimental observation of a broad $d$-wave shape resonance in degenerate ${}^{41}$K gas. We further measure the molecular binding energy that splits into three branches as a hallmark of $d$-wave molecules, and find that the lifetime of this many-body system is reasonably long at strongly interacting regime. From analyzing the breathing mode excited by ramping through this resonance, it suggests that a quite stable low-temperature atom and molecule mixture is produced. Putting all the evidence together, our system offers great promise to reach a $d$-wave molecular superfluid.

cond-mat.quant-gas↗

arXiv2017

Coupled Dipole Oscillations of a Mass-Imbalanced Bose and Fermi Superfluid Mixture

Recent experimental realizations of superfluid mixtures of Bose and Fermi quantum gases provide a unique platform for exploring diverse superfluid phenomena. We study dipole oscillations of a double superfluid in a cigar-shaped optical dipole trap, consisting of $^{41}$K and $^{6}$Li atoms with a large mass imbalance, where the oscillations of the bosonic and fermionic components are coupled via the Bose-Fermi interaction. In our high-precision measurements, the frequencies of both components are observed to be shifted from the single-species ones, and exhibit unusual features. The frequency shifts of the $^{41}$K component are upward (downward) in the radial (axial) direction, whereas the $^{6}$Li component has down-shifted frequencies in both directions. Most strikingly, as the interaction strength is varied, the frequency shifts display a resonant-like behavior in both directions, for both species, and around a similar location at the BCS side of fermionic superfluid. These rich phenomena challenge theoretical understanding of superfluids.

cond-mat.quant-gas↗

arXiv2017

A quantum degenerate Bose-Fermi mixture of $^{41}$K and $^6$Li

We report a new apparatus for the study of two-species quantum degenerate mixture of $^{41}$K and $^6$Li atoms. We develop and combine several advanced cooling techniques to achieve both large atom number and high phase space density of the two-species atom clouds. Furthermore, we build a high-efficiency two-species magnetic transport system to transfer atom clouds from the 3D magneto-optical-trap chamber to a full glass science chamber of extreme high vacuum environment and good optical access. We perform a forced radio-frequency evaporative cooling for $^{41}$K atoms while the $^6$Li atoms are sympathetically cooled in an optically-plugged magnetic trap. Finally, we achieve the simultaneous quantum degeneracy for the $^{41}$K and $^6$Li atoms. The Bose-Einstein condensate of $^{41}$K has 1.4$\times$10$^5$ atoms with a condensate fraction of about 62%, while the degenerate Fermi gas of $^6$Li has a total atom number of 5.4$\times$10$^5$ at 0.25 Fermi temperature.

cond-mat.quant-gas↗

arXiv2016

Narrow-linewidth cooling of $^{6}$Li atoms using the 2S-3P transition

We report on a narrow-linewidth cooling of $^{6}$Li atoms using the $2S_{1/2}\to 3P_{3/2}$ transition in the ultraviolet (UV) wavelength regime. By combining the traditional red magneto-optical trap (MOT) at 671 nm and the UV MOT at 323 nm, we obtain a cold sample of $1.3\times10^9$ atoms with a temperature of 58 $μ$K. Furthermore, we demonstrate a high efficiency magnetic transport for $^{6}$Li atoms with the help of the UV MOT. Finally, we obtain $8.1\times10^8$ atoms with a temperature of 296 $μ$K at a magnetic gradient of 198 G/cm in the science chamber with a good vacuum environment and large optical access.

cond-mat.quant-gas↗

arXiv2016

Production of large $^{41}$K Bose-Einstein condensates using D1 gray molasses

We use D1 gray molasses to achieve Bose-Einstein condensation of a large number of $^{41}$K atoms in an optical dipole trap. By combining a new configuration of compressed-MOT with D1 gray molasses, we obtain a cold sample of $2.4\times10^9$ atoms with a temperature as low as 42 $μ$K. After magnetically transferring the atoms into the final glass cell, we perform a two-stage evaporative cooling. A condensate with up to $1.2\times10^6$ atoms in the lowest Zeeman state $|F=1,m_F=1\rangle$ is achieved in the optical dipole trap. Furthermore, we observe two narrow Feshbach resonances in the lowest hyperfine channel, which are in good agreement with theoretical predictions.

cond-mat.quant-gas↗

arXiv2016

Observation of two-species vortex lattices in a mixture of mass-imbalance Bose and Fermi superfluids

The superfluid mixture of interacting Bose and Fermi species is a remarkable many-body quantum system. Dilute degenerate atomic gases, especially for two species of distinct masses, are excellent candidates for exploring fundamental features of superfluid mixture. However, producing a mass-imbalance Bose-Fermi superfluid mixture, providing an unambiguous visual proof of two-species superfluidity and probing inter-species interaction effects remain challenging. Here, we report the realization of a two-species superfluid of lithium-6 and potassium-41. By rotating the dilute gases, we observe the simultaneous existence of vortex lattices in both species, and thus present a definitive visual evidence for the simultaneous superfluidity of the two species. Pronounced effects of the inter-species interaction are demonstrated through a series of precision measurements on the formation and decay of two-species vortices. Our system provides a new platform for studying novel macroscopic quantum phenomena in vortex matter of interacting species.

cond-mat.quant-gas↗

arXiv2012

Experimental demonstration of topological error correction

Scalable quantum computing can only be achieved if qubits are manipulated fault-tolerantly. Topological error correction - a novel method which combines topological quantum computing and quantum error correction - possesses the highest known tolerable error rate for a local architecture. This scheme makes use of cluster states with topological properties and requires only nearest-neighbour interactions. Here we report the first experimental demonstration of topological error correction with an eight-photon cluster state. It is shown that a correlation can be protected against a single error on any qubit, and when all qubits are simultaneously subjected to errors with equal probability, the effective error rate can be significantly reduced. This demonstrates the viability of topological error correction. Our work represents the first experimental effort to achieve fault-tolerant quantum information processing by exploring the topological properties of quantum states.

quant-ph↗