A microwave two-photon radiation device and a method for detecting weak magnetic fields.

Abstract

This invention discloses a device for generating microwave two-photon radiation and a method for detecting weak magnetic fields. To further enhance the application of microwave photons in quantum information processes, we propose a method for realizing two-photon radiation. This method differs from previous two-level systems that interact with the environment, absorbing or emitting only one photon. We construct a three-level system using a Josephson structure, placing the single-photon process in a highly detuned state while the two-photon process resonates. Therefore, both photons are absorbed or released simultaneously, significantly improving radiation efficiency. Combined with the inherent single-photon dissipation, this method will be applied in chip-based quantum information processes and high-precision quantum precision measurements. The minimum detection accuracy of weak magnetic fields can reach 10 Gauss, an order of magnitude improvement over measurements using single-photon radiation mechanisms.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement technology, specifically to a device for generating microwave two-photon radiation and a method for detecting weak magnetic fields. Background Technology

[0002] Microwave photon manipulation technology has seen widespread application in recent years. Thanks to advancements in solid-state system microfabrication techniques, such as Josephson junctions, device sizes have gradually shrunk, enabling the demonstration and manipulation of quantum behaviors using these systems. In recent years, superconducting systems have been considered one of the most promising candidate systems for realizing quantum information processes, thus their coherent manipulation is of great significance.

[0003] Coplanar waveguide resonators are carriers of microwave photons. In past research, the dissipation of microwave photons due to the interaction between the cavity and the external environment has been controllable. The photon dissipation rate can be controlled by manipulating the environmental spectral function. However, current control methods mainly focus on single-photon dissipation, where individual microwave photons couple with the environment and dissipate one by one. In such systems, the photon radiation rate is relatively low, and most of the emitted photon states are classical single-photon states.

[0004] Compared to single-photon radiation, two-photon radiation has wider applications in quantum information processes and quantum precision measurement. In quantum information processes, two-photon radiation generates non-classical photon states, which can be used for high-fidelity long-distance quantum communication. In quantum precision measurement, magnetic measurements play an important role in geomagnetic navigation and mineral exploration. However, the measurement accuracy of single-photon-based methods is limited. By using two-photon radiation as the physical resource for measurement, we can improve measurement accuracy and accelerate the application of quantum technology in both military and civilian fields. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of single microwave photons coupling with the environment and dissipating into the environment one by one, resulting in a relatively low photon radiation rate, and to provide a device for generating microwave two-photon radiation and a method for detecting weak magnetic fields.

[0006] A device for generating microwave two-photon radiation includes: a DC power supply, a circuit for generating operating magnetic flux, and three... Three-layer Josephson structure, superconducting transmission line resonator, computer and oscilloscope; Josephson structure coupled with superconducting transmission line resonator;

[0007] The three mentioned The three-layer Josephson structure consists of one large knot and two small knots, with a thickness ratio of 1.4 to 1.8:1 between the large and small knots; the three knots are connected in series to form a closed loop (e.g., ...). Figure 1 (as shown)

[0008] Numerical diagonalization of the Hamiltonian of the system was performed using MATLAB to obtain the three lowest energy levels: the ground state |g>, the metastable state |f>, and the excited state |e>. The order of these three energy levels from highest to lowest is: ground state frequency < metastable state frequency < excited state frequency. Plotting the magnetic flux through the loop for these three energy levels revealed a significant energy difference between the lowest three energy levels and the higher energy levels. This magnetic flux is referred to as the "working flux".

[0009] The energy level difference between the ground state and metastable state, and between the metastable state and the excited state, results in a frequency detuning of the resonant cavity at 2% of its own frequency;

[0010] The superconducting transmission line resonant cavity is a coplanar waveguide resonant cavity;

[0011] The resonant frequency of the resonant cavity is 4-6 GHz;

[0012] The Josephson structure is located at the antinode of the coplanar waveguide resonant cavity, which is the position where the electric field intensity distribution is strongest.

[0013] The coupling strength between the Josephson structure and the superconducting transmission line resonator is 10% of the detuning strength.

[0014] The Josephson structure is capacitively coupled to the superconducting transmission line resonant cavity.

[0015] The substrate of the superconducting transmission line resonant cavity is a silicon wafer.

[0016] The large junction thickness is 1500 Å, the small junction thickness is 1000 Å, the single-photon detuning is 200 MHz, the coupling Rabi frequency is 20 MHz, the coupling time between the Josephson junction system and the superconducting transmission line resonator is 40 ms, and the decoupling time is 400 ms.

[0017] A method for generating microwave two-photon radiation, comprising:

[0018] 1) Using one of the microwave two-photon radiation generating devices described above, the Josephson junction system is cooled to its quantum ground state;

[0019] 2) Using computer control, a π / 4 pulse is applied between the ground state and the excited state of the Josephson junction system to form a superposition state;

[0020] 3) By adjusting the power supply current through the computer, the magnetic flux is made to work, at which point the coplanar waveguide resonant cavity and the Jofenson junction system are coupled to each other;

[0021] 4) Adjust the power supply current again to make the magnetic flux deviate from the working magnetic flux. At this time, the coplanar waveguide resonant cavity and Josephson structure are decoupled. The decoupling time is about 10 times the coupling time.

[0022] 5) Repeat steps 1) and 2) to restore the Josephson junction to its pre-coupling quantum state;

[0023] 6) Repeat steps 3)-4) 800-1000 times to obtain stable microwave two-photon radiation.

[0024] A method for detecting weak magnetic fields includes: covering the aforementioned microwave two-photon radiation generating device with a diamagnetic non-metallic cover, employing a method for generating microwave two-photon radiation to obtain a stable working magnetic flux for microwave two-photon radiation, and removing the diamagnetic non-metallic cover.

[0025] After removing the cover, cover it again, repeating this process several times.

[0026] This invention provides a device for generating microwave two-photon radiation and a method for detecting weak magnetic fields. To further enhance the application of microwave photons in quantum information processes, we propose a method for realizing two-photon radiation. This method differs from previous two-level systems that interact with the environment, absorbing or emitting only one photon. We construct a three-level system using a Josephson structure, placing the single-photon process in a highly detuned state while the two-photon process resonates. Therefore, both photons are absorbed or released simultaneously, significantly improving radiation efficiency. Combined with the inherent single-photon dissipation, this will be applied in chip-based quantum information processes and high-precision quantum precision measurements. The minimum detection precision of weak magnetic fields can reach 10 Gauss, an order of magnitude improvement over measurements using single-photon radiation mechanisms. Attached Figure Description

[0027] Figure 1 A model diagram of the Josephson structure coupled with a superconducting transmission line resonant cavity, which is used to generate microwave two-photon dissipation.

[0028] Figure 2 Schematic diagram of a device for generating microwave two-photon radiation;

[0029] Figure 3 This is a schematic diagram of the energy levels in microwave two-photon radiation. The eigenfrequency of the coplanar waveguide resonant cavity. and These represent single-photon detuning of the Josephson junction and microwave photons, respectively.

[0030] Figure 4 Comparison diagram of the principle of the microwave two-photon radiation scheme (a) of the present invention and the previous single-photon radiation scheme (b). Detailed Implementation

[0031] Example 1: A device for generating microwave two-photon radiation

[0032] Reference Figure 1 , 2 As shown (where Figure 1 For model diagram, Figure 2 (Diagram of the device) A device for generating microwave two-photon radiation includes: a DC power supply, a circuit for generating working magnetic flux, and three... Three-layer Josephson structure, switch, superconducting transmission line resonator, computer and oscilloscope; Josephson structure coupled to superconducting transmission line resonator;

[0033] The three mentioned The three-layer Josephson structure consists of one large knot and two small knots, with the thickness ratio of the large knot to the small knots being 1.4 to 1.8:1; the three knots are connected in series to form a closed loop.

[0034] The Hamiltonian of the system was numerically diagonalized using MATLAB to obtain the three lowest energy levels: the ground state |g>, the metastable state |f>, and the excited state |e>. The order of these three energy levels is: ground state frequency < metastable state frequency < excited state frequency. The energy levels were plotted as a function of the magnetic flux through the loop (e.g., ...). Figure 1 As shown in the figure, the three lowest energy levels have a large energy difference with the higher energy levels. The magnetic flux at this point is called the "working magnetic flux".

[0035] The energy level difference between the ground state and metastable state, and between the metastable state and the excited state, is related to the frequency detuning of the resonant cavity at 2 (1.8–2.1)% of its own frequency.

[0036] The superconducting transmission line resonant cavity is a coplanar waveguide resonant cavity;

[0037] The resonant frequency of the resonant cavity is 4-6 GHz;

[0038] The Josephson structure is located at the antinode of the coplanar waveguide resonant cavity, which is the position where the electric field intensity distribution is strongest.

[0039] The coupling strength between the Josephson structure and the superconducting transmission line resonator is 10 (9-11)% of the detuning.

[0040] The Josephson structure is capacitively coupled to the superconducting transmission line resonant cavity.

[0041] The substrate of the superconducting transmission line resonant cavity is a silicon wafer.

[0042] The large junction thickness is 1500 Å, the small junction thickness is 1000 Å, the single-photon detuning is 200 MHz, and the coupling Rabi frequency is 20 MHz.

[0043] The operation and principle are as follows:

[0044] 1. A section of superconducting transmission line forms a coplanar waveguide resonant cavity, such as... Figure 2 The curved section has two triangles on either side forming its boundaries. The resonant frequency of this resonant cavity can be measured using the output spectrum method, typically between 4-6 GHz. Furthermore, based on the cavity length and resonant frequency, the electromagnetic field distribution can be simulated using finite element analysis methods in MATLAB software to locate antinodes and nodes.

[0045] 2. A superconducting circuit consisting of three Josephson junctions, each junction is constructed as follows: A heterojunction. The magnetic flux passing through it can be adjusted using an external power supply and coils. First, the Hamiltonian of the system is numerically diagonalized using MATLAB to obtain the relationship between the energy levels of the three lowest energy levels (ground state |g>, metastable state |f>, and excited state |e>) and the magnetic flux, thus determining the working magnetic flux (defined as the magnetic flux at which the three lowest energy levels can be separated from other higher energy levels, as mentioned earlier). Then, the current is directly controlled via a computer terminal to adjust the magnitude of the magnetic flux, so that the energy level differences between the ground state and metastable state, and between the metastable state and excited state, are approximately 2% of the frequency detuning of the resonant cavity.

[0046] 3. Place the Josephson junction system at the antinode of the coplanar waveguide resonant cavity, and adjust the spacing so that the coupling strength between the junction and the cavity is 10% detuned. Under the operating magnetic flux, the microwave photons in the cavity exhibit dispersive coupling with the induced ground state and metastable state, as well as with the metastable state and excited state, under conditions of large detuning. However, the ground state and excited state satisfy the two-photon resonance condition, such as... Figure 3 As shown. Under these conditions, a Josephson junction in the excited state can simultaneously emit two microwave photons and transition to the ground state, as illustrated in the diagram. Figure 4 As shown in (a), this two-photon transition process will greatly increase the photon generation rate. Simultaneously, as indicated by the Hamiltonian in the figure, a nonlinear process of parametric down-conversion occurs, which will generate a compressed optical field. This non-classical state will contribute to the realization of quantum precision measurement. In previous single-photon radiation processes (such as...), Figure 4 (b) utilizes only two energy levels for microwave photonic resonant coupling, radiating one photon at a time, resulting in a non-classical photonic state in the final steady state. Ultimately, the number of photons radiated outward from the coplanar waveguide resonant cavity is read by an oscilloscope, with the signal intensity on the oscilloscope proportional to the number of radiated photons. For precision measurements, this method can only achieve accuracy within the classical limit. In contrast, our method's measurement accuracy approaches the Heisenberg limit.

[0047] Example 2: A method for generating microwave two-photon radiation

[0048] A method for generating microwave two-photon radiation, comprising:

[0049] 1. Using one of the microwave two-photon radiation generating devices described above, the Josephson junction system is cooled to its quantum ground state using a dilute magnetic cryostat;

[0050] 2. Using computer control, apply a π / 4 pulse between the ground state and excited state of the Josephson junction system to create a superposition state;

[0051] 3. By adjusting the power supply current through the computer, the magnetic flux is made to work, at which point the coplanar waveguide resonant cavity and the Jofenson junction system are coupled to each other;

[0052] 4. Adjust the power supply current again to make the magnetic flux deviate from the working magnetic flux. At this time, the coplanar waveguide resonant cavity and Josephson structure are decoupled. The decoupling time is about 10 times the coupling time.

[0053] 5. Repeat steps 1) and 2) to restore the Josephson junction to its pre-coupling quantum state;

[0054] 6. Repeat steps 3)-4) 800-1000 times to obtain stable microwave two-photon radiation.

[0055] Example 3: Detection of Weak Magnetic Fields

[0056] 1. The feasible parameters are as follows: large junction thickness 1500A, small junction thickness 1000A, single-photon detuning 200MHz, coupling Rabi frequency 20MHz, operating current (i.e., the current intensity that generates the operating magnetic flux) 15mA, switch-off time (i.e., under operating magnetic flux conditions) 40ms, and switch-on time (i.e., under conditions deviating from the operating magnetic flux conditions) 400ms.

[0057] 2. From a practical application perspective, this device can be used for geomagnetic detection, exploration of magnetic mineral resources, and detection of weak magnetic fields. The specific implementation process is as follows: First, the working magnetic flux of the Josephson junction system is measured, and it is calculated as follows: This magnetic flux can be achieved using either an electric current source or a magnet. Prepare a non-metallic, antimagnetic shield (hereinafter referred to as the "shield"), and... Figure 2 The image shows a microwave two-photon radiation generating device placed near the survey area. A cover is placed over the device, and the process is repeated 800-1000 times. When the cover is on, the magnetic flux generated by the mineral (denoted as...) The flux through the Josephson junction loop will not pass through it, and the system is in operating flux mode. At this time, the coupling between the Josephson junction and the coplanar waveguide resonant cavity is activated. When the cover is removed, the flux through the Josephson junction loop is... At this point, the system is under non-operating magnetic flux, and the coupling between the Josephson junction and the coplanar waveguide resonant cavity is shut off. Repeating these two steps several times yields stable two-photon radiation in the coplanar waveguide resonant cavity. The number of radiated photons is read using an oscilloscope, and then curve fitting is performed using MATLAB to obtain... Remove the previously obtained working magnetic flux from it. The magnetic flux obtained from magnetic minerals can then be obtained. .

[0058] 3. The accuracy of the microwave two-photon radiation process measurement system in this proposed scheme will be an order of magnitude higher than that of previous two-photon radiation process measurements.

[0059] The minimum accuracy for detecting weak magnetic fields can reach 10 Gauss.

Claims

1. A device for generating microwave two-photon radiation, comprising: DC power supply, circuit for generating working magnetic flux, three Al-AlO X -Al three-layer Josephson structure, superconducting transmission line resonator, computer and oscilloscope; Josephson structure coupled with superconducting transmission line resonator; The three Al-AlO X -Al The three-layer Josephson structure consists of one large knot and two small knots, with the thickness ratio of the large knot to the small knots being 1.4 to 1.8:1; the three knots are connected in series to form a closed loop. The Hamiltonian of the system was numerically diagonalized using MATLAB to obtain the three lowest energy levels: the ground state |g>, the metastable state |f>, and the excited state |e>. The order of these three energy levels is: ground state frequency < metastable state frequency < excited state frequency. Plot the relationship between the positions of the three energy levels and the magnetic flux to determine the working magnetic flux; the working magnetic flux is the magnetic flux at which the three lowest energy levels can be separated from the other higher energy levels. Under the operating magnetic flux, the microwave photons in the resonant cavity are all dispersive coupled with the induced ground state and metastable state, as well as with the metastable state and excited state, under large detuning conditions; the ground state and excited state satisfy the two-photon resonance condition.

2. The microwave two-photon radiation generating device according to claim 1, characterized in that: The energy level difference between the ground state and metastable state, and between the metastable state and the excited state, is detuned to the frequency of the resonant cavity at 1.8-2.2% of its own frequency; the superconducting transmission line resonant cavity is a coplanar waveguide resonant cavity.

3. The microwave two-photon radiation generating device according to claim 2, characterized in that: The Josephson structure is located at the antinode of the coplanar waveguide resonant cavity.

4. The microwave two-photon radiation generating device according to claim 3, characterized in that: The coupling strength between the Josephson structure and the superconducting transmission line resonant cavity is 9-11% of the detuning strength.

5. A microwave two-photon radiation generating device according to claim 4, characterized in that: The Josephson structure is capacitively coupled to the superconducting transmission line resonant cavity.

6. A microwave two-photon radiation generating device according to claim 5, characterized in that: The substrate of the superconducting transmission line resonant cavity is a silicon wafer.

7. A microwave two-photon radiation generating device according to claim 6, characterized in that: The resonant frequency of the resonant cavity is 4-6 GHz.

8. A device for generating microwave two-photon radiation according to claim 7, characterized in that: The large junction thickness is 1500 Å, the small junction thickness is 1000 Å, the single-photon detuning is 200 MHz, the coupling Rabi frequency is 20 MHz, the switching off time is 40 ms, and the switching on time is 400 ms.

9. A method for generating microwave two-photon radiation, comprising: 1) Using the microwave two-photon radiation generating device as described in claim 1, the Josephson junction system is cooled to its quantum ground state; 2) Using computer control, a π / 4 pulse is applied between the ground state and the excited state of the Josephson junction system to form a superposition state; 3) By adjusting the power supply current through the computer, the magnetic flux is made to work, at which point the coplanar waveguide resonant cavity and the Josephson junction system are coupled to each other; 4) Adjust the power supply current again to make the magnetic flux deviate from the working magnetic flux. At this time, the coplanar waveguide resonator and the Josephson structure are decoupled. The decoupling time is 9-11 times the coupling time. 5) Repeat steps 1) and 2); 6) Repeat steps 3)-4) 800-1000 times to obtain stable microwave two-photon radiation.

10. A method for detecting weak magnetic fields, comprising: The microwave two-photon radiation generating device of claim 1 is covered with a non-metallic cover with an antimagnetic coating, and a method for generating microwave two-photon radiation is adopted to obtain a stable working magnetic flux for microwave two-photon radiation. The antimagnetic non-metallic cover is then removed.

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