arXiv subjects

Kaifeng Cui

Publications and source records attributed to Kaifeng Cui.

11 recordsLinked to original sources

arXiv2026

Experimental Demonstration of a Measurement-Feedback Quantum Information Engine

Harnessing finite-time nonadiabatic transitions that are conventionally associated with quantum inner friction for useful work extraction remains an open experimental challenge. Here we address this issue by introducing and experimentally realizing an innovative measurement-feedback quantum information engine model in the trapped 40Ca+ ion system, in which the projective measurement replaces the hot reservoir as a nonthermal energy source and the feedback control conditionally steers the system through either unitary compression-expansion strokes or thermalization. We experimentally show that the repeated feedback cycle converges to a stable operating regime with a resolved energetic balance, and, by controlling the measurement angle and stroke duration, measurement-induced coherence and the finite-time nonadiabatic contribution can enhance work extraction and raise the efficiency above the corresponding Otto benchmark. The experimental results further show that, over finite ranges of stroke durations, the efficiency and intrinsic cycle power can increase simultaneously. Our experiment establishes a route toward information-to-work quantum engines that convert finite-time irreversibility into performance-enhancing resources.

quant-ph↗

arXiv2024

A Single-Ion Information Engine for Charging Quantum Battery

Information engines produce mechanical work through measurement and adaptive control. For information engines, the principal challenge lies in how to store the generated work for subsequent utilization. Here, we report an experimental demonstration where quantized mechanical motion serves as a quantum battery and gets charged in repeated cycles by a single trapped-ion information engine. This is enabled by a key technological advancement in rapid state discrimination, allowing us to suppress measurement-induced disturbances. Consequently, we were able to obtain a charging efficiency over 50\% of the theoretical limit at the optimal temperature. The experimental results substantiate that this approach can render trapped ions a promising platform for microscopic information engines with potential applications in the future upon scaling up.

quant-ph↗

arXiv2023

Demonstration of chronometric leveling using transportable optical clocks beyond laser coherence limit

Optical clock network requires the establishment of optical frequency transmission link between multiple optical clocks, utilizing narrow linewidth lasers. Despite achieving link noise levels of 10${^{-20}}$, the final accuracy is limited by the phase noise of the clock laser. Correlation spectroscopy is developed to transmit frequency information between two optical clocks directly, enabling optical clock comparison beyond the phase noise limit of clock lasers, and significantly enhancing the measurement accuracy or shorten the measurement time. In this letter, two compact transportable ${^{40}}$Ca${^+}$ clocks are employed to accomplish the correlation spectroscopy comparison, demonstrating an 10 cm level measurement accuracy of chronometric leveling using a mediocre clock laser with linewidth of 200 Hz. The relative frequency instability reaches $6.0\times10{^{-15}}/\sqrt{τ/s}$, which is about 20 times better than the result with Rabi spectroscopy using the same clock laser. This research greatly reduces the harsh requirements on the performance of the clock laser, so that an ordinary stable-laser can also be employed in the construction of optical clock network, which is essential for the field applications, especially for the chronometric leveling.

physics.optics↗

arXiv2023

Enhancement of Quantum Sensing in a Cavity Optomechanical System around Quantum Critical Point

The precision of quantum sensing could be improved by exploiting quantum phase transitions, where the physical quantity tends to diverge when the system approaches the quantum critical point. This critical enhancement phenomenon has been applied to the quantum Rabi model in a dynamic framework, showing a promising sensing enhancement without the need for complex initial state preparation. In this work, we present a quantum phase transition in the coupling cavity-mechanical oscillator system when the coupling strength crosses a critical point, determined by the effective detuning of cavity and frequency of mechanical mode. By utilizing this critical phenomenon, we obtain a prominent enhancement of quantum sensing, such as the position and momentum of the mechanical oscillator. This result provides an alternative method to enhance the quantum sensing of some physical quantities, such as mass, charge, and weak force, in a large mass system.

quant-ph↗

arXiv2022

Evaluation of the systematic shifts of a ${}^{40}\textrm{Ca}^+-{}^{27}\textrm{Al}^+$ optical clock

Quantum-logic-based ${}^{27}\textrm{Al}^+$ optical clock has been demonstrated in several schemes as there are different choices of the auxiliary ion species. In this paper, we present the first detailed evaluation of the systematic shift and the total uncertainty of an ${}^{27}\textrm{Al}^+$ optical clock sympathetically cooled by a ${}^{40}\textrm{Ca}^+$ ion. The total systematic uncertainty of the ${}^{40}\textrm{Ca}^+ - {}^{27}\textrm{Al}^+$ quantum logic clock has been estimated to be $7.9 \times 10^{-18}$, which was mainly limited by the uncertainty of the quadratic Zeeman shift. By comparing the frequency of two counter-propagating clock beams on the same ion, we measured the frequency stability to be $3.7 \times 10^{-14} /\sqrtτ$.

physics.atom-ph↗

arXiv2022

Scalable quantum logic spectroscopy

In quantum logic spectroscopy (QLS), one species of trapped ion is used as a sensor to detect the state of an otherwise inaccessible ion species. This extends precision measurements to a broader class of atomic and molecular systems for applications like atomic clocks and tests of fundamental physics. Here, we develop a new technique based on a Schrödinger cat interferometer to address the problem of scaling QLS to larger ion numbers. We demonstrate the basic features of this method using various combinations of $^{25}\text{Mg}^+$ logic ions and $^{27}\text{Al}^+$ spectroscopy ions. We observe higher detection efficiency by increasing the number of $^{25}\text{Mg}^+$ ions. Applied to multiple $^{27}\text{Al}^+$, this method will improve the stability of high-accuracy optical clocks and could enable Heisenberg-limited QLS.

physics.atom-ph↗

arXiv2019

Phase transition of spacetime: particles as black holes in anti-de Sitter space

In this work, we re-examined the ancient complex metric in the recent quantum picture of black holes as Bose-Einstein condensates of gravitons. Both black holes and particles can be described by the complex Kerr-Newman metric in a 6-D complex space, which appears as a 4-D spacetime for a real or imaginary observer because of the barrier of the horizon. As two kind of complex black holes, particle and black hole are complex conjugated and can convert into each other through a phase transition. From the view of an observer in 3-D real space, an elementary particle with spin appears as an imaginary black hole in an anti-de Sitter space. The self-gravitational interaction of a particle as an imaginary black hole makes it obtain its wave-like nature in 4-D spacetime.

physics.gen-ph↗

arXiv2019

Fluctuation and Inertia

In this work, using Jacobson's idea: '$δ$Q=TdS hold for all the local Rindler causal horizons through each spacetime point', we found that the transitions between the excited and ground state of a particle in a linear acceleration satisfy the fluctuation theorem. The up transition from the ground state to the excited state is an entropy-decreasing process, which requires an external force to contribute equal entropy increase to satisfy the second law of thermodynamics.

gr-qc↗

arXiv2019

Surface tension of the horizon

The idea of treating the horizon of a black hole as a stretched membrane with surface tension has a long history. In this work, we discuss the microscopic origin of the surface tension of the horizon in quantum pictures of spaces, which are Bose-Einstein condensates of gravitons. The horizon is a phase interface of gravitons, the surface tension of which is found to be a result of the difference in the strength of the interaction between the gravitons on its two sides. The gravitational source, such as a Schwarzschild black hole, creates a transitional zone by changing the energy and distribution of its surrounding gravitons. Archimedes' principle for gravity can be expressed as follows: "the gravity on an object is equal to the weight of the gravitons that it displaces."

gr-qc↗

arXiv2018

Black hole as fireplace: limited communications across the horizon

An insightful viewpoint was proposed by Susskind about AMPS firewall: the region behind the firewall does not exist and the firewall is an extension of the singularity. In this work, we provided a possible picture of this idea by combining Newman's complex metric and Dvali-Gomez BEC black holes, which are Bose-Einstein condensates of N gravitons. The inner space behind the horizon is a realized imaginary space encrusted by the real space outside the horizon. In this way, the singularity extents to the horizon to make a firewall for the infalling observer. Some gravitons escape during the fluctuation of the BEC black hole, resulting in a micro-transparent horizon which makes the firewall exposes slightly to an observer outside the horizon. This picture allows limited communications across the horizon.

hep-th↗

arXiv2016

A transportable 40Ca+ single-ion clock with $7.7\times 10^{-17}$ systematic uncertainty

A transportable optical clock refer to the $4s^2S_{1/2}-3d^2D_{5/2}$ electric quadrupole transition at 729 nm of single $^{40}Ca^+$ trapped in mini Paul trap has been developed. The physical system of $^{40}Ca^+$ optical clock is re-engineered from a bulky and complex setup to an integration of two subsystems: a compact single ion unit including ion trapping and detection modules, and a compact laser unit including laser sources, beam distributor and frequency reference modules. Apart from the electronics, the whole equipment has been constructed within a volume of 0.54 $m^3$. The systematic fractional uncertainty has been evaluated to be $7.7\times 10^{-17}$, and the Allan deviation fits to be $2.3\times {10}^{-14}/\sqrtτ$ by clock self-comparison with a probe pulse time 20 ms.

physics.atom-ph↗