WO2023065386A1 - Electric field force detection system based on single trapped ion - Google Patents

Abstract

An electric field force detection system based on a single trapped ion. The system comprises: a timing start signal module (11) and a timing termination signal module (12), which respectively provide a timing start signal and a timing termination signal for a time-to-digital conversion module; the time-to-digital conversion module (13), which is used for recording a time interval between the timing start signal and the timing termination signal, and obtaining, according to the time interval, a distribution situation of fluorescence intensity within a radio frequency cycle, wherein fluorescence is emitted by a single trapped ion; a micro-motion index determination module (14), which is used for obtaining a micro-motion index of the single trapped ion by means of performing fitting according to the distribution situation of the fluorescence intensity; and an electric field force measurement module (15), which is used for measuring, according to the micro-motion index, the magnitude of an electric field force received by the single trapped ion. By means of the electric field force detection system, a micro-motion index of a single trapped ion under the action of an additional electric field can be accurately measured, a weak electric field force of the additional electric field on the single trapped ion is accurately measured according to the micro-motion index, such that the precision exceeds an order of magnitude compared with existing schemes.

Description

An electric field force detection system based on a single trapped ion

This application claims the priority of the Chinese patent application with the application number 202111216141.3 and the title of the invention "An electric field force detection system based on a single trapped ion" submitted to the China Patent Office on October 19, 2021, the entire contents of which are incorporated by reference in this application.

technical field

The invention relates to the technical field of quantum information processing, in particular to an electric field force detection system based on a single trapped ion

Background technique

With the rapid development of information technology, quantum information processing has attracted more and more attention. High-sensitivity force sensors have a wide range of applications in the basic research of physics and engineering practice. At the forefront of science and technology such as precision nuclear magnetic resonance imaging, atomic force microscope, gravimeter, inertial navigation, testing quantum gravity, gravitational wave detection, and precise measurement of Newton's gravitational constant, the measurement and research of extremely small forces is a crucial link.

At present, micron-scale or nano-scale mechanical resonators are usually used to detect weak electric field forces generated by weak electric fields, weak magnetic fields, and light pressure. With the continuous improvement of scientific research requirements for measurement accuracy, traditional mechanical detectors are difficult to achieve higher Therefore, it is necessary to find a new measurement system to achieve higher precision electric field force measurement.

Contents of the invention

The purpose of the present invention is to provide an electric field force detection system based on a single trapped ion to solve the technical problem in the prior art that the measurement accuracy of the weak electric field force suffered by the trapped ions is not high enough.

The purpose of the present invention can be achieved through the following technical solutions:

An electric field force detection system based on a single trapped ion, comprising:

The timing start signal module is used to provide the timing start signal for the time digital conversion module;

A timing termination signal module is used to provide a timing termination signal for the time digital conversion module;

A time-to-digital conversion module, configured to record the time interval between the timing start signal and the timing termination signal, and obtain the distribution of fluorescence intensity in the radio frequency cycle according to the time interval, and the fluorescence is emitted by a single trapped ion;

The micro-motion index determination module is used to fit the distribution of the fluorescence intensity to obtain the micro-motion index of a single trapped ion, and the micro-motion is the movement of a single trapped ion deviating from the saddle point of the trapped potential under the action of an electric field force;

The electric field force measurement module is used to measure the magnitude of the electric field force suffered by a single trapped ion according to the micro-motion index.

Optionally, also include:

The displacement measurement module is used to measure the distance of a single trapped ion from the trapping saddle point under the action of the electric field force according to the micro-motion index.

Optionally, the timing start signal module includes:

A fluorescent photon generating unit, a fluorescent photon collecting unit and a timing start signal generating unit arranged in sequence;

Wherein, the fluorescent photon generating unit is used for a single trapped ion to generate fluorescent photons under the excitation of Doppler cooling laser, and the fluorescent photon generating unit includes a radio frequency electrode;

a fluorescent photon collection unit, configured to collect the fluorescent photons;

The timing start signal generating unit is configured to detect the fluorescent photons, and takes the arrival time of the detected fluorescent photons as the timing start signal of the time-to-digital conversion module.

Optionally, also include:

The in-phase capacitor arranged between the two RF electrodes is used to eliminate the micro-motion caused by the different phases of the RF fields of the two RF electrodes.

Optionally, the timing termination signal module includes:

A radio frequency signal source for transmitting radio frequency signals;

a radio frequency resonator, used to amplify the radio frequency signal emitted by the radio frequency signal source;

The timing termination signal generating unit is configured to reduce the frequency of the radio frequency signal, and use the moment when the frequency-reduced radio frequency signal reaches the termination port of the time-to-digital conversion module as the timing termination signal, and the radio frequency resonator is connected to the The radio frequency signal source is connected with the timing termination signal generation unit.

Optionally, also include:

The monitoring port connected with the radio frequency resonator is used for monitoring the actual voltage outputted by the radio frequency resonator to the radio frequency electrode.

Optionally, the monitoring port is:

A voltage divider circuit, the voltage divider circuit is composed of two capacitors with different capacities connected in series.

Optionally, one end of the voltage dividing capacitor is welded to the coil of the radio frequency resonator, and the other end is grounded.

Optionally, the fluorescent photon generation unit is an ion trap.

Optionally, the timing start signal generating unit is a photomultiplier tube.

The invention provides an electric field force detection system based on a single trapped ion, comprising: a timing start signal module, used to provide a timing start signal for the time-to-digital conversion module; a timing termination signal module, used to provide the time-to-digital conversion module Timing termination signal; time digital conversion module, used to record the time interval between the timing initiation signal and the timing termination signal, and obtain the distribution of fluorescence intensity in the radio frequency cycle according to the time interval, and the fluorescence is a single trapped ion Issued; the micro-motion index determination module is used to fit the distribution of the fluorescence intensity to obtain the micro-motion index of a single trapped ion, and the micro-movement is generated by a single trapped ion deviating from the trapping potential saddle point under the action of an electric field force The electric field force measurement module is used to measure the magnitude of the electric field force suffered by a single trapped ion according to the micro-motion index.

In view of this, the beneficial effects brought by the present invention are:

The present invention utilizes the timing start signal module to provide the timing start signal for the time-to-digital conversion module, utilizes the timing termination signal module to provide the timing termination signal for the time-to-digital conversion module, and the time-to-digital conversion module records the time interval between the timing initiation signal and the timing termination signal , the distribution of the fluorescence intensity in the radio frequency cycle under the additional electric field is collected, and the distribution of the fluorescence intensity is fitted to obtain an accurate micro-motion index. According to the micro-motion index, the weak electric field force exerted by the additional electric field on a single trapped ion is accurately measured . The present invention uses trapped ions as a high-precision and ultra-sensitive electric field force detector, and uses radio frequency photon correlation technology to measure the weak electric field force generated by the electric field on a single trapped ion, which is suitable for the detection of three-dimensional directions in nanoscale space, and the measured sensitivity An order of magnitude more than other solutions.

Description of drawings

Fig. 1 is the structural representation of electric field force detection system of the present invention;

Fig. 2 is the structural representation of timing start signal module of the present invention;

Fig. 3 is a structural schematic diagram of the timing termination signal module of the present invention;

Fig. 4 is the structural representation of blade ion trap in the embodiment of the present invention;

5 is a schematic diagram of the electrode structure of the blade ion trap in an embodiment of the present invention;

Fig. 6 is a structural schematic diagram of an embodiment of the present invention;

Fig. 7 is a radio frequency photon correlation signal and a fitting curve diagram under two different electric fields according to an embodiment of the present invention;

Fig. 8 is a schematic diagram of the dependence relationship between the micro-motion index and the applied electrode voltage in the present invention.

Detailed ways

An embodiment of the present invention provides an electric field force detection system based on a single trapped ion to solve the technical problem in the prior art that the measurement accuracy of the weak electric field force suffered by the trapped ion is not high enough.

In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the associated drawings. A preferred embodiment of the invention is shown in the drawings. However, the present invention can be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be thorough and complete.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

At present, mechanical resonators on the micrometer or nanometer scale can be used to detect weak forces generated by weak electric fields, weak magnetic fields, light pressure, etc. For example, a cantilevered A-Newton (10 ^-18 N, aN) force detector can be used for gravitational detection to detect whether it violates Newton's law of universal gravitation at the submillimeter length level. With the continuous improvement of the measurement accuracy requirements of scientific research, it is necessary to measure the force of the magnitude of ze Newton (10 ^-21 N, zN) or even unit Newton (10 ^-24 N, yN). It is difficult for traditional mechanical detectors to achieve the measurement accuracy of zezo-Newton and unit Newton, so it is necessary to find a new measurement system to achieve higher accuracy.

Trapped ions are charged, and their mass and volume are so small that they can be regarded as perfect particle probes, thereby detecting electromagnetic forces with high precision and sensitivity.

In the prior art, some people use a phase coherent Doppler velocimeter to detect trapped ions. They trap beryllium ions in a Penning trap, and use a laser to cool the beryllium ions to the state of ion crystals; externally exert an external force that changes with time As a perturbation of the system, the magnitude of the external force is measured by measuring the Doppler fluorescence change of the ion crystal, and the detection accuracy of the entire ion crystal reaches 390±150yN·Hz ^-1/2 . This method of measuring the electric field force requires multiple (about 100) ions to be cooled to the ion crystal, and the direct measurement is the fluorescence change of the entire ion crystal, so that the inferred electric field force acts on the entire ion crystal, and the detection space area is relatively large. It is impossible to effectively detect the micron-scale space, and the measurement of the electric field force is also limited to the frequency response range of the forced oscillation of the trapped ions.

In the existing schemes, some people also combine Hooke’s law in classical mechanics with the method of trapping a single ion system to measure the weak force. They use a linear Paul trap to trap a single ¹⁷⁴ Yb ⁺ , and use a laser to cool the ion to a temperature close to Doppler Ionic crystal states at cooling extreme temperatures. By building a high-resolution optical imaging system, the fluorescence imaging of ions is magnified about 400 times and imaged on the EMCCD. When the ion is disturbed by a force in a certain direction, a small displacement Δx will be generated. By fitting and comparing the images before and after the ion displacement on the EMCCD, the small displacement Δx is measured to be about 30nm. Using the simple harmonic potential well Hooke's law F=kΔx can calculate the magnitude of the weak force. The measurement accuracy of this measurement method can reach 100zN, that is, 100zN, but the adjustment of its high-magnification optical imaging system is challenging, and the nanometer-scale displacement changes require high quality imaging of a single ion, and post-image processing requires high numerical simulation. The measurement accuracy of the optical axis direction of optical imaging by image processing is relatively low, about 808±51zN·Hz ^-1/2 .

The defects of the above-mentioned weak electromagnetic force measurement method based on trapped ions severely limit the detection of trapped ions.

The invention adopts the method of measuring the fluorescence emitted by a single trapped ion, although the signal-to-noise ratio is small due to the limitation of the fluorescence intensity, and the sensitivity of the measurement force is lower than that of the phase coherent Doppler velocity measurement technology. However, the displacement of detecting a single trapped ion can reach the nanometer level, and the frequency response range that can be measured can also theoretically range from DC to the bandwidth of the detector.

The invention also measures single ion displacement and weak force, and the radio frequency photon correlation method used can improve the measurement sensitivity of displacement and weak force by about one order of magnitude compared with high-resolution imaging technology.

Referring to Fig. 1, the present invention provides an embodiment of an electric field force detection system based on a single trapped ion, including:

The timing start signal module 11 is used to provide the timing start signal for the time digital conversion module;

The timing termination signal module 12 is used for providing the timing termination signal for the time digital conversion module;

The time digital conversion module 13 is used to record the time interval between the timing start signal and the timing termination signal, and obtain the distribution of fluorescence intensity in the radio frequency cycle according to the time interval, and the fluorescence is emitted by a single trapped ion;

The micro-motion index determination module 14 is used to fit the distribution of the fluorescence intensity to obtain the micro-motion index of a single trapped ion, and the micro-motion is the movement of a single trapped ion deviating from the saddle point of the trapped potential under the action of an electric field force;

The electric field force measurement module 15 is configured to measure the magnitude of the electric field force experienced by a single trapped ion according to the micro-motion index.

Preferably, this embodiment further includes a displacement measurement module, configured to measure the distance of a single trapped ion from the trapping saddle point under the action of the electric field force according to the micro-motion index.

Please refer to Fig. 2, in the present embodiment, timing start signal module 11 comprises: fluorescent photon generating unit 111, fluorescent photon collecting unit 112 and timing starting signal generating unit 113 arranged in sequence; Wherein, fluorescent photon generating unit 111 uses A single trapped ion generates fluorescent photons under the excitation of the Doppler cooling laser, the fluorescent photon generation unit includes a radio frequency electrode; the fluorescent photon collection unit 112 is used to collect fluorescent photons; the timing start signal generation unit 113 is used to detect the For fluorescent photons, the arrival time of detected fluorescent photons is used as the timing start signal of the time-to-digital conversion module.

Referring to Fig. 3, in the present embodiment, the timing termination signal module 12 includes: a radio frequency signal source 121, used to transmit a radio frequency signal; a radio frequency resonator 122, used to amplify the radio frequency signal emitted by the radio frequency signal source; , used to reduce the frequency of the radio frequency signal, and use the moment when the frequency-reduced radio frequency signal arrives at the termination port of the time-to-digital conversion module as a timing termination signal, and the radio frequency resonator is connected with the radio frequency signal source and the radio frequency signal source respectively. The timing termination signal generation unit is connected. In a preferred embodiment, a frequency divider is used to reduce the frequency of the radio frequency signal.

In one embodiment, a monitoring port is added outside the radio frequency resonator 122, and the monitoring port is connected to the radio frequency resonator 122 for monitoring the voltage actually output from the radio frequency resonator 122 to the radio frequency electrode. In a preferred embodiment, the monitoring port is a voltage divider circuit composed of two capacitors in series, one large and one small, one end is welded on the radio frequency spiral coil, the other end is grounded, and the voltage at both ends of the large capacitor is drawn out with wires for monitoring. In a preferred embodiment, the radio frequency resonator 122 is a radio frequency spiral resonator.

The monitoring port monitors the radio frequency signal emitted by the radio frequency signal source 121, and the radio frequency signal reaches the termination port of the time-to-digital conversion module 13 after the frequency divider reduces the signal frequency, and the arrival time is used as the timing termination signal of the time-to-digital conversion module 13.

Preferably, an in-phase capacitance is added between the radio frequency electrodes of the ion trap, that is, the RF electrodes, so as to eliminate extra micro-motions caused by different phases of the radio frequency fields of the radio frequency electrodes.

In this embodiment, in the timing termination signal module 12, a monitoring port is added outside the radio frequency resonator 122, and the voltage of the radio frequency electrode can be monitored by using the voltage division ratio, so as to provide a more reliable reference for the phase information at the arrival time of the fluorescent photons. At the same time, the frequency divider is used to reduce the frequency of the timing termination signal, and the cycle of the RF photon-related signal is increased to an integer multiple of the cycle of the RF signal source. Using repeated phase information, the micro-motion index can be more accurately fitted and its uncertainty reduced. To provide reliable data for micro-displacement measurement.

It is worth noting that the radio frequency photon correlation signal is a time statistical signal of the arrival time of the fluorescent photon and the termination time of the radio frequency after the frequency divider.

In this embodiment, the radio frequency photon correlation method is used to measure the weak electric field force experienced by a single trapped ion. In the RF photon correlation method, a single trapped ion deviates from the saddle point due to the stray electric field, and there will be additional micro-motion. Because of the Doppler effect, the laser frequency experienced by a single trapped ion will change, so the fluorescence intensity emitted by a single trapped ion will be modulated by the trapped RF electric field. The greater the stray electric field force suffered by a single trapped ion, the greater its displacement from the saddle point, and the greater the additional micro-motion, the greater the modulation of the trapped radio frequency electric field. In this embodiment, the process of using the radio frequency photon correlation method to detect the extra micro-motion of a single trapped ion is as follows:

(1) Detect the fluorescent signal emitted by a single trapped ion through a photomultiplier tube, and use the arrival time of the detected fluorescent photon as the timing start signal of the time-to-digital conversion module;

(2) the moment when the radio frequency signal arrives at the termination port of the time-to-digital conversion module after the frequency divider is used as the timing termination signal;

(3) The time-to-digital conversion module records the time interval Δt between the timing start signal and the timing termination signal, and converts it into a digital signal, wherein the time interval Δt actually represents the phase of the radio frequency field corresponding to the arrival moment of the fluorescent photon, and this value appears The greater the probability of , the greater the probability of the fluorescence photon emission corresponding to this phase. After a period of measurement, the distribution of the fluorescence intensity within the radio frequency cycle can be obtained.

(4) Fitting the fluorescence intensity distribution in the radio frequency period to obtain the micro-motion index. Generally, the greater the change in fluorescence intensity, the higher the micro-motion index. It can be inferred that the greater the displacement of a single trapped ion from the saddle point, the greater the stray electric field force it receives.

It can be understood that when different voltages are applied to the electrodes of the ion trap, the simulated stray electric field force pushes a single trapped ion away from the trapping potential saddle point, and a single trapped ion generates additional micro-motion under the action of the trapping potential. Due to the existence of the Doppler effect, the laser frequency experienced by a single trapped ion will change, so the fluorescence intensity emitted by a single trapped ion will be modulated by the trapped RF electric field. The greater the stray electric field force suffered by a single trapped ion, the greater its displacement from the saddle point, and the greater the additional micro-motion, the greater the modulation of the trapped radio frequency electric field in the fluorescence signal.

After obtaining the distribution of the fluorescence intensity in the radio frequency period, the distribution of the fluorescence intensity in the radio frequency period is fitted to obtain the micro-motion index. Generally, the greater the change in fluorescence intensity, the greater the micro-motion index, and it can be inferred that the more a single trapped ion deviates from the saddle point. The resulting micromotion index can be used to measure the ultraweak force exerted by the electrostatic field on individual trapped ions.

In this embodiment, the fluorescent photon generating unit 111 may be an ion trap, for example, a blade ion trap as shown in FIG. 4 . The Doppler cooling of the trapped ions is realized by using a laser. Under the action of the Doppler cooling laser, a single trapped ion in the ion trap excites fluorescent photons, and the fluorescent photon collection unit 112 (such as a large numerical aperture objective lens) collects the fluorescent photons. Improve the collection efficiency of fluorescent photons; the timing start signal generation unit 113 (such as a photomultiplier tube) detects the fluorescent signal emitted by a single trapped ion, and uses the arrival time of the detected fluorescent photon as the timing start signal of the time-to-digital conversion module 13 .

As shown in Figure 4, the blade ion trap is divided into DC electrode and RF electrode areas, and the blade ion trap is composed of two DC electrodes and two RF electrodes. The slits on the DC blade are divided into different small-block electrodes DC1-DC10, so that the voltage on each small-block electrode is independently controlled; RF voltage RF1-RF2 and DC bias voltage DC11-DC12 are applied to the RF electrodes, and the DC electrodes are and RF electrode setup as shown in Figure 5. Compared with the traditional quadrupole ion trap, the blade ion trap can precisely apply a voltage on the more finely divided DC electrodes, and more effectively control the electric field of trapped ions. In the central region of the ion trap, its potential can be:

Among them, the first term on the right side of formula (1) represents the DC voltage component, the second term represents the RF voltage component, X(Y, Z) is the axial (radial) main axis direction of the ion trap, _VR and Ω are respectively Amplitude and frequency of the RF voltage, V _DC is the DC voltage, R is the distance between the center of the ion trap and the electrodes in the radial plane, κ′,α′,β′,γ′,κ,α,β,γ are the ion Well geometry factor.

In a typical Pual ion trap, the equation of motion for a trapped ion of mass m and charge e is given by the Mathieu equation,

Among them, μ _i is the ion displacement, and μ _i is the second derivative of the ion displacement with respect to time, that is, the acceleration; i represents the direction of the axial main axis X, or the directions of the two radial main axes Y and Z,

When |a _i |<<1 and |q _i |<<1, the first-order solution of formula (2) is:

If there is a stray electric field with component E _i in the i direction on the trapping potential, then the ion's equation of motion is modified as:

The lowest-order solution of formula (4) to q _i and a _i is:

in,

is the displacement from the equilibrium position to the saddle point of the RF field after the stray electric field is added, and u _1i is the frequency

The amplitude of the secular motion, φ _si is the phase of the secular motion determined by the initial conditions of ion position and velocity, and φ _i is the phase of the micro motion. This low-order solution shows that a small electric field or weak force eE _i can move ions u _0i and also induce additional micromotions with frequency Ω and amplitude u _0i q _i /2.

Assuming that the phase difference between the two AC electrodes is zero, the micro-motion index can be detected by the laser beam and used

to describe, where

laser wave vector,

For additional extra micro-movements.

If the detection laser is along a main axis i direction,

Among them, k is the wave vector of the Doppler cooled laser, k=2π/λ, and λ is its wavelength. Taking ytterbium ion as an example, the wavelength of the Doppler cooled laser is 369.5nm. q _i is the dimensionless q parameter of the ion trap in the i-axis direction, which is determined by the geometric structure of the ion trap and the trapping potential. The trapped ions generally work in the lowest stable region, and the typical value of q _i is 0.2. m is the mass of trapped ions, for ytterbium ion ¹⁷¹ Yb ⁺ , m=171×1.66×10 ^-27 kg. ω _i is the angular frequency of the macro motion of the ion trap in the i-axis direction, the typical value is 2π×0.5MHz.

Therefore, once β _i is determined, formula (6) can be used to calculate the micro-displacement u _0i in the direction i, and the weak electric field force in the direction F _i in the i direction.

The extra micro-motion of trapped ions due to the stray electric field will cause the first-order Doppler effect, which will significantly change the excited fluorescence spectrum of trapped ions. Assume that the electric field of the exciting laser has amplitude E ₀ , frequency ω _L , phase

and wave vector k, then the laser field can be expressed as:

Among them, u' is the additional micro-motion, and the Fourier transform is applied to the formula (7), and the laser spectral electric field intensity E(ω) in the case of β<<1 is approximated as follows:

E(ω)∝J ₀ (β)δ(ω-ω _L )+J ₁ (β)[δ(ω-ω _L -Ω _RF )-δ(ω-ω _L +Ω _RF )] (8)

Under the condition of low light intensity I<<I _sat saturation light intensity, ion transitions can be described as classically damped harmonic oscillators with central angular frequency ω ₀ and damping ratio Γ (transition linewidth). Its frequency response to excitation at frequency ω is:

Therefore, using the inverse Fourier transform, the individual ion fluorescence detected by the photomultiplier tube is:

Among them, J ₀ and J ₁ are Bessel functions of the 0th order and 1st order respectively, E(ω) is the spectral electric field intensity of the excitation laser in the moving ion reference system, A is the ion fluorescence spectral intensity, Δ=ω -ω ₀ =-Γ is the detuning between the excitation laser frequency and ion resonance frequency, which can be locked by stabilizing the Doppler cooling laser frequency through iodine saturation absorption spectrum, so that the red detuning is equal to the ion transition linewidth. t is the time recorded by the time-to-digital converter. phase

and

can be substituted into numerical calculations. A ^* is the complex conjugate function of A, and Ω _rf is the angular frequency of the trapped ion radio frequency electric field. In the case of micro-motion index β<<1,

Item can be ignored.

According to formula (10), the micro-motion index can be fitted from the experimental data S recorded by a time-to-digital converter (TDC), and then the weak electric field force applied to a single ion and the resulting micro-displacement can be determined from formula (6).

In this embodiment, by designing the laser to propagate from the direction of the main axis of ion movement, collecting the fluorescence emitted by the interaction between a single trapped ion and the laser, establishing radio frequency photon correlation statistics, and analyzing the movement of a single trapped ion in the direction of the main axis, to realize the generation of a single trapped ion. For the measurement of Newton's ultraweak force, the spatial sensitivity of the detection can reach the nanometer level in the direction of the main axis of ion motion. Technically, three beams of laser beams in the direction of the main axis of ion motion can be used to measure the zezo-Newton ultraweak force generated by a three-dimensional electric field on a single trapped ion, and the spatial sensitivity of the detection can reach the nanometer level in the three-dimensional direction.

Please refer to Fig. 6, another embodiment of the electric field force detection system based on a single trapped ion provided by the present invention, wherein, the ion trap includes a DC electrode and an RF electrode, that is, a radio frequency electrode, and the single trapped ion in the ion trap is cooled by Doppler Fluorescent photons are generated under the excitation of the laser, and the fluorescent photon collection system is connected with the ion trap to collect the fluorescent photons emitted by the trapped ions; the photomultiplier tube uses the arrival time of the detected fluorescent photons as the timing start signal of the time-to-digital converter; A monitoring port is added outside the device. The monitoring port is a voltage divider circuit composed of two capacitors with different capacities in series to monitor the actual voltage output from the RF spiral resonator to the RF electrode. A single trapped ion is formed by deviating from the trapping potential saddle point due to the existence of an additional electric field. Additional micro-motions; add in-phase capacitance between the two RF electrodes to eliminate additional micro-motions due to the different phases of the RF field of the RF electrodes; the RF electrodes in the ion trap are connected to the RF helical resonator, and the RF helical resonator The monitoring signal of the monitoring signal arrives at the end port of the time-to-digital converter after passing through the frequency divider, and the moment when the radio frequency signal arrives at the end port of the time-to-digital converter is used as the timing termination signal of the time-to-digital converter; the time-to-digital conversion module records the timing start signal and timing The time interval of the termination signal is collected to obtain the distribution of the fluorescence intensity in the radio frequency cycle; the micro-motion index of a single trapped ion is obtained by fitting according to the distribution of the fluorescence intensity, and the electric field force of a single trapped ion is measured according to the micro-motion index And the micro-displacement produced under the action of electric field force.

In this embodiment, a monitoring port for the radio frequency spiral resonator is added, and the voltage of the radio frequency electrode can be monitored by using the voltage dividing ratio, so as to provide a more reliable reference for the phase information at the arrival time of the fluorescent photons. At the same time, the frequency divider is used to reduce the frequency of the termination signal, and the cycle of the RF photon-related signal is increased to an integer multiple of the cycle of the RF signal source. Using repeated phase information, the micro-motion index can be more accurately fitted and its uncertainty reduced. It provides reliable data for the measurement of micro-displacement and weak electric field force.

Please refer to FIG. 7 . In one embodiment, the RF photon correlation signals and fitting curves collected by the time-to-digital conversion module under two different electric fields are shown in FIG. 7 .

The time recording unit Time bin of the time-to-digital converter is 216ps. The black box represents the fluorescent signal collected by the time-to-digital conversion module under an electric field, the solid line is the fitting curve, and the fitting micro-motion index β1=0.0306±0.0028. Hollow circles and dotted lines are fluorescence signals and fitting curves under another electric field, and the fitting micromotion index β2=0.0030±0.0026.

Using the formula (10), it is possible to fit the radio-frequency photon correlation signal of the hollow circle in Fig. 7, and obtain the minimum value of the micro-motion index β=0.0030±0.0026, it can be considered that the ion is already at the saddle point of the trapping potential under the measurement accuracy, and its value is also On the same order of magnitude as other literature reports. When changing the trapping electrode voltage, the greater the voltage change relative to the trapping potential saddle point, the greater the additional electric field force on the ions, and the farther the distance they are pushed. The greater the additional micro-motion of ions in the new equilibrium position, the higher the micro-motion index, as shown in the radio-frequency photon correlation signal of the black box in Figure 7, the micro-motion index β=0.0306±0.0028 is obtained.

In this embodiment, the electric field force detection system shown in Figure 6 uses the same phase capacitance to ensure that the phases on the two radio frequency electrodes are the same, assuming that the Doppler cooling laser is incident along one of the main axis directions of the ion movement, such as the i direction, it can be used Equation (6) calculates the displacement u _0i of ions shifting from the trapped saddle point under the action of the additional electric field force, and the formula determines the size of the additional electric field force F _i :

Among them, k is the wave vector of the Doppler cooled laser, k=2π/λ, and λ is its wavelength. Taking ytterbium ion as an example, the wavelength of the Doppler cooled laser is 369.5nm. q _i is the dimensionless q parameter of the ion trap in the i-axis direction, which is determined by the geometric structure of the ion trap and the trapping potential. The trapped ions generally work in the lowest stable region, and the typical value of q _i is 0.2. m is the mass of trapped ions, for ytterbium ion ¹⁷¹ Yb ⁺ , m=171×1.66×10 ^-27 kg. ω _i is the angular frequency of the macro motion of the ion trap in the i-axis direction, and the typical value is 2π×0.5MHz.

In this embodiment, the displacement u _0i of a single trapped ion under action can be measured by using the radio frequency photon correlation method, so that a single trapped ion probe can be effectively used to realize sensitive electric field detection in a nanoscale space. Using the fitting data obtained in Figure 7, using the formula (6) and the above numerical estimates, under different voltages, the distances of the trapped ions from the saddle point of the trapping potential are about 1.8±1.6nm and 18.0±1.6nm respectively, and the direction Keep consistent with the direction of the main axis of ion movement i pointed by the laser. Through the measurement of the three main axis directions, the spatial sensitivity of its detection can reach the nanometer level.

Likewise, using the formula (6), the present invention uses the micro-motion index to deduce the additional weak electric field force F _i applied in this direction. According to the data in Figure 7, under the measurement time of 100s, under different electric fields, the additional electric field force on a single trapped ion is about 4.9±4.3zN and 50.4±4.6zN respectively, and the corresponding detection sensitivity is 49±43zN Hz ^-1/2 .

In one embodiment, the dependence relationship between the micro-motion index and the applied electrode voltage is shown in Fig. 8, and Fig. 8 also shows the relationship between the micro-motion index and the applied electrode voltage by using formula (6). Different voltages were applied on electrodes 2 and 7 to push individual trapped ions away from the saddle point of the trapping potential, and the histogram of fluorescence was recorded using a time-to-digital converter, and the micromotion index was fitted by Equation (10). Then the micro-displacement of a single trapped ion and the applied weak electric field force can be deduced from formula (6). Figure 8 proves that the weak electric field force is proportional to the change of the applied voltage, and the direction of the electric field force on both sides of the trapped potential saddle point is opposite.

FIG. 8 shows the dependence of the micromotion index β _i on the voltage applied to electrodes 2 and 7 . Among them, V7=V2+0.25V. The solid line is the fit of equation (6). The histogram measured by the time-to-digital conversion module at V2=11.75V is the hollow circle in Figure 7, and the histogram measured by the time-to-digital conversion module at V2=12.25V is the solid box in Figure 7, and the corresponding micro-motion indices are respectively β _i =0.0030±0.0026, β _i =0.0306±0.0028; the corresponding applied electric field force can be estimated as 4.9zN, 50.4zN. The additional micro-motion index and the applied electric field force corresponding to the remaining points can also be obtained separately. The slope of the two straight lines with V2=11.75V as the intersection represents the positive and negative directions of the electric field force along the main axis.

The electric field force detection system based on a single trapped ion provided by the embodiment of the present invention uses a single trapped ion to detect a weak electric field force. The specific process is: use laser to realize Doppler cooling of single trapped ion, optimize the electrode design of ion trap, so that the trapped single ion can respond sensitively to the additional electromagnetic field; use iodine saturation non-Doppler effect absorption spectrum to stabilize the laser frequency Operation, reduce the fluctuation of detuning amount between laser frequency and ion transition frequency, provide stable parameters for micro-motion index; use large numerical aperture objective lens to optimize ion fluorescence collection efficiency, provide initial signal for radio frequency photon correlation method; improve the circuit of radio frequency resonator , to eliminate the phase influence on the RF electrode; use the RF signal after the frequency division circuit to provide a stop signal for the RF photon correlation method; use the time-to-digital conversion module to record the time interval between the start signal and the stop signal, and count the fluorescence in two RF cycles The distribution of the strength; the micro-motion index is obtained by fitting, so as to infer the spatial information of the magnitude and action of the weak electric field force.

The electric field force detection system based on a single trapped ion provided in this embodiment, by designing the laser to propagate from the direction of the main axis of ion movement, collects the fluorescent photons emitted by the interaction between a single trapped ion and the laser, establishes radio frequency photon correlation statistics, and analyzes the The movement in the direction of the main axis realizes the measurement of the zezo-Newton quantum ultraweak force suffered by a single trapped ion, and the spatial sensitivity of the detection can reach the nanometer level in the direction of the main axis of ion movement. Technically, three beams of laser beams in the direction of the main axis of ion motion can be used to measure the zezo-Newton ultra-weak force of a single trapped ion by a three-dimensional electric field, and the spatial sensitivity of the detection can reach the nanometer level in the three-dimensional direction.

This embodiment uses trapped ions as high-precision and ultra-sensitive electric field force detectors, and uses radio frequency photon correlation technology to measure the weak electric field force generated by the electric field on a single trapped ion, which is suitable for the detection of three-dimensional directions in nanoscale space. The sensitivity estimation can reach 49±43zN·Hz ^-1/2 , and the measurement accuracy is an order of magnitude higher than that of the single-ion super-resolution imaging scheme.

In the radio frequency photon correlation method, the invention uses the first-order Doppler effect to detect the extra micro-motion of a single trapped ion. According to the vector characteristic of the motion of a single trapped ion, its motion direction can be projected along the main axis direction determined by the trapped potential. Since the Doppler effect only exists in the direction of the laser wave vector, the measured micro-motion oscillation direction and the displacement direction away from the trapped saddle point are actually pointed by the laser. The present invention proposes to use laser beams to measure the main axis direction of the movement of a single trapped ion, so as to determine its displacement from the saddle point caused by the additional electric field and determine the magnitude of the additional electric field force.

The invention records for the first time the radio frequency photon correlation signal diagram of multiple radio frequency periods, and fits the micro-motion index. For the first time, the technical scheme of using the micro-motion index to measure the micro-displacement of a single trapped ion in the direction of the main axis of motion and the applied weak electric field force is realized, and the detection of the micro-displacement of a single trapped ion in the three-dimensional direction of the nanometer level and the level of Newton level is realized. sensitivity.

The invention improves the radio-frequency photon correlation technology, and proves in principle that it can measure the super-weak force of zezo-Newton generated by the additional electric field force on a single trapped ion, the detection space sensitivity can reach the nanometer level in the three-dimensional direction, and the sensitivity of the measured weak electric field force exceeds An order of magnitude larger than the original single-ion scheme. The solution proposed by the invention can realize the high-precision measurement of the weak electric field force of the Newton magnitude in the nanometer scale.

The electric field force detection system based on a single trapped ion provided in this embodiment improves the radio frequency photon correlation method to accurately measure the micro-motion index of a single trapped ion, and uses the micro-motion index to accurately measure the weak electric field force exerted by an additional electric field on a single trapped ion, The micro-motion index can also be used to accurately measure the micro-displacement of a single trapped ion under the action of an electric field force.

It is worth noting that if there is an imaging device with broadband and high quantum efficiency, a similar technical solution can be adopted to replace the photomultiplier tube and time-to-digital converter in the present invention with a high-speed and high-quantum efficiency imaging device, and use image processing and radio frequency correlation Combined methods, higher detection sensitivity can be achieved for individual trapped ions. In the prior art, the external modulation of ions is macro-motion (on the order of 100 kHz), and the electric field force detection system based on a single trapped ion provided in this embodiment can measure the micro-motion modulation of ions (on the order of 10 MHz), realizing a more sensitive Detection of individual trapped ions.

Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working process of the above-described system, device and unit can refer to the corresponding process in the foregoing method embodiment, and will not be repeated here.

In the embodiments provided in this application, it should be understood that the disclosed systems, devices and methods may be implemented in other ways. For example, the device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or May be integrated into another system, or some features may be ignored, or not implemented. In another point, the mutual coupling or direct coupling or communication connection shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be in electrical, mechanical or other forms.

The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, each unit may exist separately physically, or two or more units may be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

If the integrated unit is realized in the form of a software function unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium , including several instructions to make a computer device (which may be a personal computer, a server, or a network device, etc.) execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage media include: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disk or optical disc, etc., which can store program codes. .

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. An electric field force detection system based on a single trapped ion, characterized in that it includes:

   The timing start signal module is used to provide the timing start signal for the time digital conversion module;

   A timing termination signal module is used to provide a timing termination signal for the time digital conversion module;

   A time-to-digital conversion module, configured to record the time interval between the timing start signal and the timing termination signal, and obtain the distribution of fluorescence intensity in the radio frequency cycle according to the time interval, and the fluorescence is emitted by a single trapped ion;

   The micro-motion index determination module is used to fit the distribution of the fluorescence intensity to obtain the micro-motion index of a single trapped ion, and the micro-motion is the movement of a single trapped ion deviating from the saddle point of the trapped potential under the action of an electric field force;

   The electric field force measurement module is used to measure the magnitude of the electric field force suffered by a single trapped ion according to the micro-motion index.
2. The electric field force detection system based on a single trapped ion according to claim 1, further comprising:

   The displacement measurement module is used to measure the distance of a single trapped ion from the trapping saddle point under the action of the electric field force according to the micro-motion index.
3. The electric field force detection system based on a single trapped ion according to claim 1, wherein the timing start signal module comprises:

   A fluorescent photon generating unit, a fluorescent photon collecting unit and a timing start signal generating unit arranged in sequence;

   Wherein, the fluorescent photon generating unit is used for a single trapped ion to generate fluorescent photons under the excitation of Doppler cooling laser, and the fluorescent photon generating unit includes a radio frequency electrode;

   a fluorescent photon collection unit, configured to collect the fluorescent photons;

   The timing start signal generating unit is configured to detect the fluorescent photons, and takes the arrival time of the detected fluorescent photons as the timing start signal of the time-to-digital conversion module.
4. The electric field force detection system based on a single trapped ion according to claim 3, further comprising:

   The in-phase capacitor arranged between the two RF electrodes is used to eliminate the micro-motion caused by the different phases of the RF fields of the two RF electrodes.
5. The electric field force detection system based on a single trapped ion according to claim 1, wherein the timing termination signal module comprises:

   A radio frequency signal source for transmitting radio frequency signals;

   a radio frequency resonator, used to amplify the radio frequency signal emitted by the radio frequency signal source;

   The timing termination signal generating unit is configured to reduce the frequency of the radio frequency signal, and use the moment when the frequency-reduced radio frequency signal reaches the termination port of the time-to-digital conversion module as the timing termination signal, and the radio frequency resonator is connected to the The radio frequency signal source is connected with the timing termination signal generation unit.
6. The electric field force detection system based on a single trapped ion according to claim 5, further comprising:

   The monitoring port connected with the radio frequency resonator is used for monitoring the actual voltage outputted by the radio frequency resonator to the radio frequency electrode.
7. The electric field force detection system based on a single trapped ion according to claim 6, wherein the monitoring port is:

   A voltage divider circuit, the voltage divider circuit is composed of two capacitors with different capacities connected in series.
8. The electric field detection system based on a single trapped ion according to claim 7, wherein one end of the voltage dividing capacitor is welded to the coil of the radio frequency resonator, and the other end is grounded.
9. The electric field force detection system based on a single trapped ion according to claim 1, wherein the fluorescent photon generation unit is an ion trap.
10. The electric field force detection system based on a single trapped ion according to claim 1, wherein the timing start signal generating unit is a photomultiplier tube.

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