A quantum dot contact reading device for a topological qubit and a preparation method thereof

Abstract

The application discloses a quantum dot contact reading device of a topological quantum bit and a preparation method thereof. The device comprises a semiconductor nanowire, a quantum dot contact structure, a source electrode and a drain electrode, a gate electrode and a reading circuit. The method comprises the following steps: preparing the semiconductor nanowire on a substrate, preparing the quantum dot contact structure at a predetermined position, preparing the source electrode and the drain electrode, preparing the gate electrode and connecting the reading circuit. The application realizes high-sensitivity and rapid reading of the topological quantum bit, the quantum dot contact conductance is proportional to the Majorana zero mode projection weight, the reading time is not more than 10 nanoseconds, and the application can be widely applied to the fields of quantum state reading and multi-quantum bit parallel measurement of topological quantum computing.

Description

Technical Field

[0001] This invention relates to the fields of quantum computing and quantum measurement technology, specifically to a quantum dot contact readout device for topological qubits and its fabrication method. This invention is particularly applicable to scenarios involving the readout of Majorana zero modes, measurement of projected weights of topological qubits, verification of quantum gate operation results, and detection of error syndromes in quantum error correction. Background Technology

[0002] Quantum state readout is a crucial step in achieving closed-loop control in quantum computing. In topological quantum computing, quantum state information is encoded by the non-Abelian statistical properties of Majorana zero modes, and the readout method differs fundamentally from that of traditional qubits. Quantum dot contact is one of the most promising schemes for reading Majorana zero mode quantum states—detecting the occupied state of Majorana zero modes by measuring changes in the conductivity of the quantum dot contact. However, existing quantum dot contact readout devices face significant challenges in terms of sensitivity, integration, and scalability. Existing point-to-point contact reading technologies can be mainly classified into the following categories: (a) Single quantum dot contact reading A single quantum dot contact is fabricated at or near one end of a nanowire, and the presence of Majorana zero modes is determined by measuring the change in its conductivity. This approach has the following problems: (1) the signal-to-noise ratio of a single quantum dot contact is low, making it difficult to distinguish quantum states; (2) the conductivity signal is significantly affected by environmental charge noise; (3) the readout speed is slow, limited by the response time of the quantum dot contact; and (4) multi-bit parallel readout cannot be achieved. (ii) Dual quantum dot contact differential readout Two quantum dot contacts are used to form a differential measurement structure to eliminate common-mode noise. This type of scheme has the following problems: (1) the fabrication of the two quantum dot contacts requires extremely high precision consistency; (2) the calibration of the differential signal is complex; (3) the device size is large, which is not conducive to large-scale integration; (4) the readout speed is still limited. (III) Quantum Dot Contact Array Readout Quantum dot contact arrays are fabricated at multiple nodes of a nanowire network to achieve multi-bit parallel readout. This approach has the following problems: (1) severe crosstalk between quantum dot contacts; (2) difficulty in ensuring the performance consistency of each quantum dot contact in the array; (3) complex signal routing and readout circuits; and (4) complex fabrication process and low yield. (iv) Rapid readout based on radio frequency reflection method Rapid readout is achieved by measuring the impedance change of quantum dot contacts using radio frequency signal reflection. This type of scheme has the following problems: (1) it requires a high-frequency signal source and complex radio frequency circuits; (2) the radio frequency signal may interfere with the coherence of the quantum bits; (3) it is difficult to synchronize multi-channel radio frequency readout; and (4) it has high power consumption. In summary, the fundamental deficiency of existing quantum dot contact readout devices and methods lies in the lack of a topological quantum bit quantum dot contact readout device that can simultaneously achieve high sensitivity, fast readout, low crosstalk, and large-scale integration. This invention, for the first time, combines the projection weight measurement principle with quantum dot contact readout, utilizing the correspondence between quantum dot contact conductivity and projection weight to achieve direct quantum state readout. Summary of the Invention

[0003] (a) Purpose of the invention This invention provides a quantum dot contact readout device for topological qubits and its fabrication method, aiming to solve the technical problems of low sensitivity, slow readout speed, and difficulty in large-scale integration of existing quantum dot contact readout devices. (II) Technical Principles This invention is based on the principles of quantum dot contact transport and projection geometry. In this invention, the quantum state readout of a topological qubit is achieved through the following physical chain: The relationship between the conductance and projection weight of a quantum dot contact: The conductance G of a quantum dot contact is determined by the tunneling probability through the quantum dot. When a Majorana zero mode approaches the quantum dot contact, its occupied state affects the tunneling probability of the quantum dot contact, thus changing the conductance. The change in conductance ΔG is proportional to the projection weight |w|² of the Majorana zero mode; therefore, the quantum state can be directly read by measuring the conductance. Differential measurement structure: A dual quantum dot contact differential structure is employed. One quantum dot contact serves as the signal channel coupled to the Majorana zero mode, while the other acts as the reference channel coupled to ambient noise. The differential signal eliminates common-mode noise and improves the signal-to-noise ratio. Fast readout mechanism: The conductivity response time of quantum dot contacts is determined by the quantum dot charging energy and tunneling rate (up to nanosecond level), which is 1-2 orders of magnitude faster than traditional readout schemes. Arrayed parallel readout: A quantum dot contact array is fabricated at multiple nodes of a nanowire network, and the state information of all qubits is acquired simultaneously through a parallel readout circuit. The fundamental difference from existing technologies: This invention is not a "single quantum dot contact + DC measurement" solution, but achieves high-sensitivity and fast reading through differential quantum point contact. (III) Technical Solution A quantum dot contact readout device for topological qubits, characterized in that it comprises: Semiconductor nanowires disposed on a substrate, comprising at least one Majorana zero mode; A quantum dot contact structure is disposed at a predetermined position on the semiconductor nanowire and coupled to the Majorana zero mode; The source and drain are respectively disposed on both sides of the quantum dot contact structure for applying bias voltage and measuring conductivity; A gate electrode is disposed above the quantum dot contact structure and is used to control the barrier height of the quantum dot contact. A readout circuit, connected to the source and drain, is used to measure conductance changes and output quantum state information. A method for fabricating a quantum dot contact readout device for topological qubits, characterized by comprising the following steps: S1: Fabrication of semiconductor nanowires on a substrate; S2: Prepare quantum dot contact structures at predetermined locations on semiconductor nanowires; S3: Fabricate source and drain electrodes on both sides of the quantum dot contact structure; S4: Fabricate a gate electrode above the quantum dot contact structure; S5: Connect the reading circuit to complete the quantum dot contact reading device. (iv) Beneficial effects First, the conductivity of quantum dot contacts is sensitive to Majorana zero-mode quantum states, enabling high-sensitivity readout. Second, the differential measurement structure eliminates common-mode noise, improving the signal-to-noise ratio by more than 5 times. Third, it has a fast read speed with a response time of no more than 10 nanoseconds. Fourth, the quantum dot contact structure is compatible with CMOS processes, supporting large-scale array integration. Fifth, it can read multiple qubits in parallel, meeting the needs of large-scale quantum computing. Detailed Implementation

[0004] (a) Purpose of the invention This invention provides a quantum dot contact readout device for topological qubits and its fabrication method, aiming to solve the technical problems of low sensitivity, slow readout speed, and difficulty in large-scale integration of existing quantum dot contact readout devices. (II) Technical Principles This invention is based on the principles of quantum dot contact transport and projection geometry. In this invention, the quantum state readout of a topological qubit is achieved through the following physical chain: The relationship between the conductance and projection weight of a quantum dot contact: The conductance G of a quantum dot contact is determined by the tunneling probability through the quantum dot. When a Majorana zero mode approaches the quantum dot contact, its occupied state affects the tunneling probability of the quantum dot contact, thus changing the conductance. The change in conductance ΔG is proportional to the projection weight |w|² of the Majorana zero mode; therefore, the quantum state can be directly read by measuring the conductance. Differential measurement structure: A dual quantum dot contact differential structure is employed. One quantum dot contact serves as the signal channel coupled to the Majorana zero mode, while the other acts as the reference channel coupled to ambient noise. The differential signal eliminates common-mode noise and improves the signal-to-noise ratio. Fast readout mechanism: The conductivity response time of quantum dot contacts is determined by the quantum dot charging energy and tunneling rate (up to nanosecond level), which is 1-2 orders of magnitude faster than traditional readout schemes. Arrayed parallel readout: A quantum dot contact array is fabricated at multiple nodes of a nanowire network, and the state information of all qubits is acquired simultaneously through a parallel readout circuit. The fundamental difference from existing technologies: This invention is not a "single quantum dot contact + DC measurement" solution, but achieves high-sensitivity and fast reading through differential quantum point contact. (III) Technical Solution A quantum dot contact readout device for topological qubits, characterized in that it comprises: Semiconductor nanowires disposed on a substrate, comprising at least one Majorana zero mode; A quantum dot contact structure is disposed at a predetermined position on the semiconductor nanowire and coupled to the Majorana zero mode; The source and drain are respectively disposed on both sides of the quantum dot contact structure for applying bias voltage and measuring conductivity; A gate electrode is disposed above the quantum dot contact structure and is used to control the barrier height of the quantum dot contact. A readout circuit, connected to the source and drain, is used to measure conductance changes and output quantum state information. A method for fabricating a quantum dot contact readout device for topological qubits, characterized by comprising the following steps: S1: Fabrication of semiconductor nanowires on a substrate; S2: Prepare quantum dot contact structures at predetermined locations on semiconductor nanowires; S3: Fabricate source and drain electrodes on both sides of the quantum dot contact structure; S4: Fabricate a gate electrode above the quantum dot contact structure; S5: Connect the reading circuit to complete the quantum dot contact reading device. (iv) Beneficial effects First, the conductivity of quantum dot contacts is sensitive to Majorana zero-mode quantum states, enabling high-sensitivity readout. Second, the differential measurement structure eliminates common-mode noise, improving the signal-to-noise ratio by more than 5 times. Third, it has a fast read speed with a response time of no more than 10 nanoseconds. Fourth, the quantum dot contact structure is compatible with CMOS processes, supporting large-scale array integration. Fifth, it can read multiple qubits in parallel, meeting the needs of large-scale quantum computing. IV. Detailed Implementation Example 1 (Single Quantum Dot Contact Reading Device) Step 1: Fabrication of semiconductor nanowires. InAs nanowires with diameters of 80-120 nm were grown on a substrate by molecular beam epitaxy. Step 2: Prepare quantum dot contact structures. Quantum dot contact structures are formed at predetermined locations on nanowires using electron beam lithography and shallow etching. The quantum dots have a diameter of 50-100 nm. Step 3: Prepare the source and drain electrodes. Ti / Au electrodes were deposited on both sides of the quantum dot contact structure by electron beam evaporation with a spacing of 100-200 nm. Step 4: Prepare the gate electrode. An Al2O3 gate insulating layer (5-10 nm thick) is deposited on top of the quantum dot contact structure, and then a Ti / Au gate electrode is fabricated. Step 5: Connect the reading circuit. By connecting the source and drain to a low-noise current amplifier and an analog-to-digital converter, the quantum state is read out by measuring changes in conductance. Example 2 (Differential dual quantum dot contact readout device) Two identical quantum dot contact structures were fabricated, one coupled to a Majorana zero mode (signal channel) and the other isolated from a Majorana zero mode (reference channel). The difference in conductivity between the two quantum dot contacts was measured to eliminate common-mode noise. Example 3 (Parallel Readout of Quantum Dot Contact Array) A quantum dot contact array is fabricated at multiple nodes of a nanowire network, with each quantum dot contact independently connected to a readout circuit, enabling parallel readout of multiple qubits. Example 4 (Fast RF Readout) An RF reflection measurement module is integrated into the readout circuit to quickly read the quantum state by measuring the change in the RF reflection coefficient of the quantum dot contact, with a readout time of no more than 1 ns. Attached Figure Description

[0005] Figure 1 This is a schematic diagram of the overall structure of the quantum dot contact readout device for the topological qubit of the present invention. Figure 2 This is a schematic diagram illustrating the principle of quantum dot contact and Majorana zero-mode coupling in this invention. Figure 3 This is a schematic diagram of the differential dual quantum dot contact readout structure of the present invention. Figure 4 This is a flowchart of the preparation method of the quantum dot contact reading device of the present invention. Figure 5 This is a schematic diagram of a typical application scenario of the present invention. Terminology Explanation

[0006] Quantum dot contact: A quantum structure consisting of a narrow channel between two electrodes, whose conductivity varies with gate voltage and neighboring quantum states through quantized tunneling effect. Majorana zero mode: The zero-energy Majorana bound state that appears in topological superconductors, which is the physical carrier of topological qubits. Differential readout: A readout method that eliminates common-mode noise by using two differential measurements with identical structures.

Claims

1. Claim 1: A quantum dot contact readout device for topological qubits, characterized in that, include: Semiconductor nanowires disposed on a substrate, comprising at least one Majorana zero mode; A quantum dot contact structure is disposed at a predetermined position on the semiconductor nanowire and coupled to the Majorana zero mode; The source and drain are respectively disposed on both sides of the quantum dot contact structure for applying bias voltage and measuring conductivity; A gate electrode is disposed above the quantum dot contact structure and is used to control the barrier height of the quantum dot contact. A readout circuit, connected to the source and drain, is used to measure conductance changes and output quantum state information.

2. Claim 2: The apparatus according to claim 1, characterized in that, The semiconductor nanowires are made of at least one of InAs, InSb, or InP, and have a diameter of 30-200 nm.

3. Claim 3: The apparatus according to claim 1, characterized in that, The quantum dot contact structure has a quantum dot diameter of 20-100 nm and a distance of 10-100 nm from the Majorana zero mode.

4. Claim 4: The apparatus according to claim 1, characterized in that, The change in conductivity ΔG of the quantum dot contact is proportional to the projection weight |w|² of the Majorana zero mode, and the quantum state is read by measuring the change in conductivity.

5. Claim 5: The apparatus according to claim 1, characterized in that, The reading time of the reading circuit is no more than 10 nanoseconds.

6. Claim 6: A method for fabricating a quantum dot contact readout device for topological qubits, characterized in that, Includes the following steps: S1: Fabrication of semiconductor nanowires on a substrate; S2: Prepare quantum dot contact structures at predetermined locations on semiconductor nanowires; S3: Fabricate source and drain electrodes on both sides of the quantum dot contact structure; S4: Fabricate a gate electrode above the quantum dot contact structure; S5: Connect the reading circuit to complete the quantum dot contact reading device.

7. Claim 7: The method according to claim 6, characterized in that, The quantum dot contact structure described in step S2 is prepared using electron beam lithography and shallow etching processes, with an etching depth of 30%-70% of the nanowire diameter.

8. Claim 8: The method according to claim 6, characterized in that, The device also includes a reference quantum dot contact structure, which forms a differential measurement pair with the quantum dot contact structure.

9. Claim 9: The apparatus according to claim 1, characterized in that, The device is an array structure containing multiple quantum dot contact structures, each corresponding to a majorana zero mode, enabling parallel readout of multiple qubits.

10. Claim 10: The apparatus according to claim 1, characterized in that, The reading circuit includes a radio frequency reflection measurement module, which achieves rapid reading by measuring changes in the radio frequency reflection coefficient.

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