Multi-quantum dot coupling device and preparation method thereof

Abstract

The present invention discloses a multi-quantum dot coupling device and its preparation method. The multi-quantum dot coupling device comprises a microdisk microcavity and several quantum dots located within the microdisk microcavity. The microdisk microcavity exhibits a degenerate optical whispering gallery mode, and the quantum dots are located at the antinodes of the optical whispering gallery mode of the microdisk microcavity. The wavelengths of the transitional luminescence emitted by the several quantum dots are the same or similar. The microdisk microcavity has a smooth and symmetrical surface and comprises a dielectric disk. Implementation of the present invention can improve the coupling efficiency between quantum nodes and has broad application in the field of quantum communication technology.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication technology, and in particular to a multi-quantum dot coupling device and a preparation method thereof. Background Art

[0002] Quantum information technology, the integration of quantum physics and information technology, will profoundly transform the future information industry and usher in a new information technology revolution. As one of the key applications of quantum information technology, quantum computing can significantly increase computational speed and has significant strategic significance for national defense, security, and socioeconomic development.

[0003] Achieving quantum information processing requires the establishment of a quantum network. A quantum network consists of quantum nodes and quantum channels. Quantum nodes are responsible for preparing, processing, and storing quantum states; quantum channels are responsible for transmitting quantum states between quantum nodes with high fidelity and achieving distributed entanglement across the entire network. A common approach to implementing a quantum network is to couple quantum dots with optical microcavities to form quantum nodes, then connect multiple optical microcavities with waveguides to form a quantum network. However, the inherent losses in the waveguides and the losses associated with the coupling between the waveguides and quantum nodes severely reduce the coupling efficiency between quantum nodes, which decreases dramatically with the number of quantum nodes. Summary of the Invention

[0004] In view of this, an object of an embodiment of the present invention is to provide a multi-quantum dot coupling device and a preparation method thereof, which can improve the coupling efficiency between quantum nodes.

[0005] In a first aspect, an embodiment of the present invention provides a multi-quantum dot coupling device, comprising a microdisk microcavity and a plurality of quantum dots located within the microdisk microcavity, wherein the microdisk microcavity has a degenerate optical whispering gallery mode, the quantum dots are located at the antinode position of the optical whispering gallery mode of the microdisk microcavity, the wavelengths of the transitional luminescence of the plurality of quantum dots are the same or similar, the surface of the microdisk microcavity is smooth and symmetrical, and the microdisk microcavity comprises a dielectric disk.

[0006] Optionally, the degenerate optical whispering gallery mode includes a clockwise traveling wave mode and a counterclockwise traveling wave mode.

[0007] Optionally, the material of the micro-disk microcavity includes gallium arsenide or silicon dioxide.

[0008] Optionally, the diameter of the micro-disk micro-cavity ranges from 1 μm to 2.5 μm, and the thickness of the micro-disk micro-cavity ranges from 0.1 μm to 0.3 μm.

[0009] In a second aspect, an embodiment of the present invention provides a method for preparing a multi-quantum dot coupling device, comprising:

[0010] preparing a micro-disk micro-cavity, wherein the surface of the micro-disk micro-cavity is smooth and symmetrical;

[0011] Growing quantum dots with the same or similar transition wavelengths;

[0012] Several quantum dots are prepared at the antinode position of the optical whispering gallery mode of the microdisk microcavity.

[0013] Optionally, the preparation of the micro-disk micro-cavity specifically includes:

[0014] Micro-columns are prepared on a substrate by using femtosecond laser etching, and the edges of the micro-columns are ground using a focused ion beam to obtain micro-disk micro-cavities.

[0015] Optionally, the growing of quantum dots having the same or similar transition wavelengths specifically includes:

[0016] The quantum dot sample is grown on the gallium arsenide sample by molecular beam epitaxy. The structure of the quantum dot sample includes Al 0.8 Ga 0.2 As sacrificial layer, GaAs layer, Al 0.4 Ga 0.6 As layer and GaAs cap layer;

[0017] Al by local droplet etching process 0.4 Ga 0.6 A layer of low-density GaAs quantum dots is embedded in the middle of the As layer;

[0018] At a preset substrate temperature, the Al 0.4 Ga 0.6 Aluminum droplets are deposited on the surface of the As layer and annealed to obtain nanopores;

[0019] GaAs with a preset thickness is grown on the nanohole and annealed to obtain a GaAs sheet containing GaAs quantum dots.

[0020] Optionally, the step of preparing a plurality of quantum dots at antinode positions of the optical whispering gallery mode of the microdisk microcavity specifically includes:

[0021] On a GaAs wafer containing GaAs quantum dots, electron beam lithography and lift-off processes are used to create positioning marks for the quantum dots.

[0022] Using fluorescence imaging technology to obtain the spatial position of the quantum dot relative to the positioning mark;

[0023] Measure the photoluminescence spectrum of the target quantum dots;

[0024] The antinode position of the micro-disk microcavity is determined according to the spatial position and the photoluminescence spectrum, and the microcavity structure is prepared by adopting electron beam lithography and dry etching processes.

[0025] Optionally, the preparation method further comprises:

[0026] The transition wavelengths of multiple quantum dots are tuned to be consistent through multi-external field control technology.

[0027] Optionally, the step of tuning the transition wavelengths of a plurality of quantum dots to be consistent by using a control technology specifically includes:

[0028] A nanostructure containing quantum dots is placed on a biaxial piezoelectric ceramic substrate, a certain voltage is applied to generate stress, and the nanostructure is subjected to stress stretching to change the structure of the quantum dots;

[0029] and / or preparing quantum dots grown by molecular beam epitaxy into devices, connecting them to an external circuit via leads, and applying an electric field to the quantum dots by applying a voltage via the external circuit;

[0030] And / or applying longitudinal magnetic field and transverse magnetic field to the nanostructure of quantum dots.

[0031] Implementation of the embodiments of the present invention provides the following beneficial effects: In this embodiment, multiple quantum dots within a microdisk microcavity are located at antinodes of the optical whispering gallery mode of the microdisk microcavity. The quantum dots emit light at transition wavelengths that are identical or similar, forming a resonance with the microdisk microcavity. A quantum dot at an antinode strongly couples with photons to form a quantum node. The quantum nodes are coupled to each other through the optical whispering gallery mode of the same microdisk microcavity. Multiple antinodes enable strong coupling of multiple quantum nodes with the microcavity mode, achieving strong coupling of multiple quantum dots through a single microdisk microcavity without waveguide loss, thereby improving the coupling efficiency between quantum nodes. The smooth and symmetrical surface of the microdisk microcavity gives the microdisk microcavity a high quality factor, significantly reducing photon loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the structure of a quantum network in a related technology provided by an embodiment of the present invention;

[0033] Figure 2 (a) is a schematic structural diagram of a microdisk microcavity including two traveling wave modes provided by an embodiment of the present invention; Figure 2 (b) is a light field distribution diagram of a standing wave mode provided by an embodiment of the present invention; Figure 2 (c) is a distribution diagram of quantum dots provided by an embodiment of the present invention;

[0034] Figure 3 This is a radial electric field distribution diagram of a specific multi-quantum dot coupling device provided by an embodiment of the present invention;

[0035] Figure 4 The figure is a schematic flow chart of the steps of a method for preparing a multi-quantum dot coupling device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are provided for ease of description only and do not limit the order of the steps. The order of execution of the steps in the embodiments can be adaptively adjusted based on the understanding of those skilled in the art.

[0037] See Figure 1 A quantum network consists of quantum nodes and quantum channels. Quantum nodes are responsible for the preparation, processing, and storage of quantum states, while quantum channels are responsible for the transmission of quantum states between quantum nodes. The physical implementation platform for quantum nodes is a cavity quantum electrodynamics system composed of two-level systems such as optical microcavities and quantum dots. Quantum dots have two quantum states: the ground state and the excited state. When an electron transitions from the excited state to the ground state, it emits a photon. Conversely, a quantum dot can absorb a photon and transition from the ground state to the excited state. When a quantum dot is placed in a microcavity with a high quality factor, the photon emitted by the quantum dot during the transition can be localized in the microcavity for a long time before being reabsorbed by the quantum dot. This strong coupling between the photon and the quantum dot makes it possible to manipulate the quantum state of the quantum dot using photons. Quantum nodes composed of strongly coupled optical microcavities and quantum dots are connected through waveguides. The waveguides can transmit photons from one quantum node to another, thereby enabling the transmission of quantum states between different quantum nodes and, in turn, achieving distributed entanglement across the entire quantum network to realize quantum information processing capabilities.

[0038] An embodiment of the present invention provides a multi-quantum dot coupling device, comprising a microdisk microcavity and a plurality of quantum dots located within the microdisk microcavity. The microdisk microcavity has a degenerate optical whispering gallery mode, the quantum dots are located at the antinodes of the optical whispering gallery mode of the microdisk microcavity, the wavelengths of transitional luminescence from the plurality of quantum dots are the same or similar, the surface of the microdisk microcavity is smooth and symmetrical, and the microdisk microcavity comprises a dielectric disk.

[0039] Specifically, a microdisk microcavity is a dielectric disk with a diameter of several microns.

[0040] In a microdisk microcavity, light is trapped within the cavity due to total internal reflection at the microdisk boundary, forming a degenerate optical whispering gallery mode. When a quantum dot is placed at the edge of the microdisk microcavity, its transitional luminescence excites two degenerate optical modes of the microdisk. These modes superimpose to form a standing wave resonance mode, whose field distribution features multiple antinodes (field intensity maxima). The field distribution characteristics of the whispering gallery mode in a microdisk microcavity make it possible to couple multiple quantum dots through a single optical microcavity mode. Precise positioning of semiconductor quantum dots allows the quantum dots to be positioned at the antinodes of the microdisk microcavity whispering gallery optical mode, achieving strong coupling between the quantum dots and the microcavity mode. Because the whispering gallery mode has multiple antinodes, strong coupling between multiple quantum dots and the microcavity mode is possible, enabling the coupling of multiple quantum dots through a single microcavity mode. The microdisk microcavity has a high quality factor, allowing photons to be localized within the microcavity for extended periods, significantly reducing photon loss. A quantum dot at an antinode strongly couples with photons to form a quantum node, which is naturally coupled to other quantum nodes through the same microcavity mode. Compared with the scheme of using waveguides to connect multiple microcavities, this scheme avoids waveguide loss, thereby efficiently realizing the mutual coupling of multiple quantum dots.

[0041] Optionally, the degenerate optical whispering gallery mode includes a clockwise traveling wave mode and a counterclockwise traveling wave mode.

[0042] See Figure 2 Schematic diagram of the field distribution of the optical whispering gallery mode of a microdisk microcavity and the coupling of multiple quantum dots through a microdisk microcavity. (a) A microdisk microcavity supports a clockwise traveling wave mode and a counterclockwise traveling wave mode. These two traveling wave modes are degenerate, that is, their resonant wavelengths are the same. When the two traveling wave modes are excited simultaneously, the two modes superimpose into a standing wave mode, and its optical field distribution is shown in Figure (b). The reddest and bluest points are the points where the absolute value of the electric field intensity is the largest (i.e., the antinode), one is positive (red is positive) and the other is negative (blue is negative). It can be seen that the field distribution of the microdisk microcavity has multiple antinode positions, so multiple quantum dots can be prepared at the antinode positions of the microdisk microcavity whispering gallery mode, so that multiple quantum dots can be coupled through a microcavity. As shown in Figure (c), the white elliptical dots represent quantum dots, which are placed at the antinode positions of the microdisk field distribution. The strong coupling between the quantum dots and the antinodes forms a quantum node, and multiple quantum nodes are naturally coupled together through a microcavity mode.

[0043] Optionally, the material of the micro-disk microcavity includes gallium arsenide or silicon dioxide.

[0044] Optionally, the diameter of the micro-disk micro-cavity ranges from 1 μm to 2.5 μm, and the thickness of the micro-disk micro-cavity ranges from 0.1 μm to 0.3 μm.

[0045] Specifically, the material of the micro-disk micro-cavity includes but is not limited to gallium arsenide or silicon dioxide. The diameter and thickness of the micro-disk micro-cavity are determined according to actual applications and are not specifically limited in this embodiment.

[0046] In a specific embodiment, the microdisk is made of gallium arsenide (GaAs), has a radius of 1.48 μm, and a thickness of 0.2 μm. This microdisk supports an optical whispering gallery resonance mode with a resonant wavelength of 1.305 μm. Theoretically, the quality factor of this mode is 1.062×10 6 , the radial electric field distribution is as follows Figure 3 shown.

[0047] Implementation of the embodiments of the present invention provides the following beneficial effects: In this embodiment, multiple quantum dots within a microdisk microcavity are located at antinodes of the optical whispering gallery mode of the microdisk microcavity. The quantum dots emit light at transition wavelengths that are identical or similar, forming a resonance with the microdisk microcavity. A quantum dot at an antinode strongly couples with photons to form a quantum node. The quantum nodes are coupled to each other through the optical whispering gallery mode of the same microdisk microcavity. Multiple antinodes enable strong coupling of multiple quantum nodes with the microcavity mode, achieving strong coupling of multiple quantum dots through a single microdisk microcavity without waveguide loss, thereby improving the coupling efficiency between quantum nodes. The smooth and symmetrical surface of the microdisk microcavity gives the microdisk microcavity a high quality factor, significantly reducing photon loss.

[0048] See Figure 4 , an embodiment of the present invention provides a method for preparing a multi-quantum dot coupling device, comprising:

[0049] S100, preparing a micro-disk micro-cavity, wherein the surface of the micro-disk micro-cavity is smooth and symmetrical;

[0050] S200, growing quantum dots with the same or similar transition wavelengths;

[0051] S300, preparing a plurality of quantum dots at the antinode position of the optical whispering gallery mode of the micro-disk microcavity.

[0052] Through high-precision micro-nanostructure fabrication technology, a microdisk microcavity with a smooth surface and good symmetry is produced, ensuring that the microdisk supports a high-quality whispering gallery optical resonance mode. Photons can be localized in the microcavity for a long time with very low photon loss. For quantum dots to couple through photons, the wavelength of the quantum dot transition emission must be the same and resonate with the optical microcavity. The quantum dot droplet epitaxial growth method can be used to grow semiconductor quantum dots with good symmetry and high isotropy. The transition wavelengths of quantum dots grown using this method are very close. The quantum dots need to be placed at the antinode position of the microdisk microcavity whispering gallery optical mode field distribution to enhance their coupling strength with photons. The quantum dots are prepared at the antinode position of the microdisk microcavity whispering gallery mode using high-precision optical positioning technology to ensure strong coupling between the quantum dots and the microcavity mode.

[0053] Optionally, the preparation of the micro-disk micro-cavity specifically includes:

[0054] S101 , preparing micro-pillars on a substrate by femtosecond laser etching, and grinding the edges of the micro-pillars by using a focused ion beam to obtain micro-disk micro-cavities.

[0055] Specifically, the substrate includes but is not limited to gallium arsenide or silicon dioxide.

[0056] In a specific embodiment, micropillars are fabricated on a sample of a gallium arsenide / silicon dioxide substrate using femtosecond laser etching, and the edges of the micropillars are polished using a focused ion beam to improve edge smoothness and thereby increase the quality factor of the optical resonance mode.

[0057] Optionally, the growing of quantum dots having the same or similar transition wavelengths specifically includes:

[0058] S201, growing a quantum dot sample on a gallium arsenide sample by molecular beam epitaxy, wherein the structure of the quantum dot sample includes Al 0.8 Ga 0.2 As sacrificial layer, GaAs layer, Al 0.4 Ga 0.6 As layer and GaAs cap layer;

[0059] S202, through the local droplet etching process on Al 0.4 Ga 0.6 A layer of low-density GaAs quantum dots is embedded in the middle of the As layer;

[0060] S203, at a preset substrate temperature, 0.4 Ga 0.6 Aluminum droplets are deposited on the surface of the As layer and annealed to obtain nanopores;

[0061] S204 , growing GaAs with a preset thickness on the nanopore, and annealing, to obtain a GaAs sheet containing GaAs quantum dots.

[0062] It should be noted that the thickness of each layer in the quantum dot sample, the annealing time, etc. are determined according to actual applications and are not specifically limited in this embodiment.

[0063] In a specific embodiment, the quantum dot sample is grown on a GaAs sample by molecular beam epitaxy; the sample structure comprises a 500 nm thick Al 0.8 Ga 0.2 As sacrificial layer, 4nm thick GaAs layer, 140nm thick Al 0.4 Ga 0.6 As layer and 4nm thick GaAs cap layer; by introducing local droplet etching process on Al0.4 Ga 0.6 A layer of low-density GaAs quantum dots is embedded in the middle of the As layer; at a substrate temperature of 640°C, the Al 0.4 Ga 0.6 A 0.5 layer of aluminum droplets was deposited on the As surface and then annealed for 5 minutes to obtain a nanopore; then 2 nm GaAs was grown on the nanopore and annealed for 5 minutes, so that highly symmetrical GaAs quantum dots could be generated through the nanopore.

[0064] Optionally, the step of preparing a plurality of quantum dots at antinode positions of the optical whispering gallery mode of the microdisk microcavity specifically includes:

[0065] S301, on a GaAs wafer containing GaAs quantum dots, using electron beam lithography and lift-off processes to produce quantum dot positioning marks;

[0066] S302, using fluorescence imaging technology to obtain the spatial position of the quantum dot relative to the positioning mark;

[0067] S303, measuring the photoluminescence spectrum of the target quantum dot;

[0068] S304 , determining the antinode position of the micro-disk microcavity according to the spatial position and the photoluminescence spectrum, and fabricating the microcavity structure by electron beam lithography and dry etching.

[0069] It should be noted that the fluorescent imaging technology, electron beam lithography, lift-off process, dry etching process, etc. can all adopt existing related technologies.

[0070] In one specific embodiment, after preparing a GaAs wafer containing multiple quantum dots, we use electron beam lithography and lift-off techniques to create positioning marks for quantum dot positioning. After creating the positioning marks on the wafer, fluorescence imaging techniques are used to determine the spatial position of the quantum dots relative to the positioning marks. The photoluminescence spectrum of the target quantum dots is measured to determine the luminescence transition wavelength of the quantum dots, which is used to design a microdisk microcavity near resonance with the quantum dots. Once the spatial and spectral information for each quantum dot is obtained, a microdisk microcavity is designed that resonates with the quantum dot and has an antinode located at the quantum dot. The microcavity structure is then fabricated using electron beam lithography and dry etching.

[0071] Optionally, the preparation method further comprises:

[0072] S400, tune the transition wavelengths of multiple quantum dots to be consistent through multi-external field control technology.

[0073] It should be noted that semiconductor quantum dots grown using molecular beam epitaxy technology may have different transition wavelengths. In order to adjust the emission wavelength of quantum dots, multiple external field control technologies can be comprehensively applied, such as stress, electric field or magnetic field.

[0074] High-quality quantum dots are grown, and their transition emission wavelengths are very close. However, it is not possible to ensure that the emission wavelengths of multiple quantum dots are completely consistent. Therefore, external fields such as stress, electric field, and magnetic field are applied to the prepared device to control the transition emission wavelengths of the quantum dots to make them consistent, so that multiple quantum dots can achieve efficient coupling through a single optical microcavity mode.

[0075] Optionally, the step of tuning the transition wavelengths of a plurality of quantum dots to be consistent by using a control technology specifically includes:

[0076] S401, placing a nanostructure containing quantum dots on a biaxial piezoelectric ceramic substrate, applying a certain voltage to generate stress, and performing stress stretching on the nanostructure to change the structure of the quantum dots;

[0077] S402, and / or preparing quantum dots grown by molecular beam epitaxy into devices, and connecting them to an external circuit via leads, and applying an electric field to the quantum dots by applying voltage via the external circuit;

[0078] S403, and / or applying a longitudinal magnetic field and a transverse magnetic field to the nanostructure of the quantum dots.

[0079] In some specific embodiments, the stress tuning method includes: placing a nanofilm containing quantum dots on a biaxial piezoelectric ceramic substrate, applying a certain voltage to generate stress, stress stretching the nanofilm, changing the structure of the quantum dots, and thus achieving regulation of the quantum dot emission wavelength. The electric field tuning method includes: preparing quantum dots grown by molecular beam epitaxy into ni-Schottky devices, and connecting them to an external circuit through leads, applying an electric field to the quantum dots by applying voltage through the external circuit, thereby achieving regulation of the quantum dot transition wavelength by the electric field. The magnetic field tuning method includes: adding a longitudinal magnetic field (Faraday magnetic field) and a transverse magnetic field (Voigt magnetic field) to the quantum dot sample. The Faraday magnetic field is a static magnetic field added along the growth direction of the quantum dots, and the Voigt magnetic field is a magnetic field added perpendicular to the growth direction of the quantum dots. The magnetic field can adjust the emission wavelength of the quantum dots by adjusting the exciton energy level.

[0080] Implementation of the embodiments of the present invention provides the following beneficial effects: In this embodiment, multiple quantum dots within a microdisk microcavity are located at antinodes of the optical whispering gallery mode of the microdisk microcavity. The quantum dots emit light at transition wavelengths that are identical or similar, forming a resonance with the microdisk microcavity. A quantum dot at an antinode strongly couples with photons to form a quantum node. The quantum nodes are coupled to each other through the optical whispering gallery mode of the same microdisk microcavity. Multiple antinodes enable strong coupling of multiple quantum nodes with the microcavity mode, achieving strong coupling of multiple quantum dots through a single microdisk microcavity without waveguide loss, thereby improving the coupling efficiency between quantum nodes. The smooth and symmetrical surface of the microdisk microcavity gives the microdisk microcavity a high quality factor, significantly reducing photon loss.

[0081] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for preparing a multi-quantum dot coupling device, characterized in that: include: preparing a micro-disk micro-cavity, wherein the surface of the micro-disk micro-cavity is smooth and symmetrical; Growing quantum dots with the same or similar transition wavelengths; Several quantum dots are prepared at the antinode position of the optical whispering gallery mode of the microdisk microcavity, including: On a sample sheet containing quantum dots, electron beam lithography and lift-off processes were used to create positioning marks for the quantum dots; Using fluorescence imaging technology to obtain the spatial position of the quantum dot relative to the positioning mark; Measure the photoluminescence spectrum of the target quantum dots; The antinode position of the micro-disk microcavity is determined according to the spatial position and the photoluminescence spectrum, and the microcavity structure is prepared by adopting electron beam lithography and dry etching processes.

2. The preparation method according to claim 1, characterized in that The preparation of the micro-disk micro-cavity specifically includes: Micro-columns are prepared on a substrate by using femtosecond laser etching, and the edges of the micro-columns are ground using a focused ion beam to obtain micro-disk micro-cavities.

3. The preparation method according to claim 1, characterized in that The growing of quantum dots having the same or similar transition wavelengths specifically includes: The quantum dot sample is grown on the gallium arsenide sample by molecular beam epitaxy. The structure of the quantum dot sample includes Al 0.8 Ga 0.2 As sacrificial layer, GaAs layer, Al 0.4 Ga 0.6 As layer and GaAs cap layer; Al by local droplet etching process 0.4 Ga 0.6 A layer of low-density GaAs quantum dots is embedded in the middle of the As layer; At a preset substrate temperature, the Al 0.4 Ga 0.6 Aluminum droplets are deposited on the surface of the As layer and annealed to obtain nanopores; GaAs with a preset thickness is grown on the nanohole and annealed to obtain a GaAs sheet containing GaAs quantum dots.

4. The preparation method according to claim 1, characterized in that The preparation method further comprises: The transition wavelengths of multiple quantum dots are tuned to be consistent through multi-external field control technology.

5. The preparation method according to claim 4, characterized in that The transition wavelengths of several quantum dots are tuned to be consistent through control technology, including: A nanostructure containing quantum dots is placed on a biaxial piezoelectric ceramic substrate, a certain voltage is applied to generate stress, and the nanostructure is subjected to stress stretching to change the structure of the quantum dots; and / or preparing quantum dots grown by molecular beam epitaxy into devices, connecting them to an external circuit via leads, and applying an electric field to the quantum dots by applying a voltage via the external circuit; And / or applying longitudinal magnetic field and transverse magnetic field to the nanostructure of quantum dots.

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