An interaction-free, single-pixel quantum imaging system for undetected photons

Abstract

The invention discloses an interaction-free, single-pixel quantum imaging system for undetected photons, which mainly comprises an induced coherence module and a single-pixel imaging module; the induced coherence module comprises a nonlinear crystal, a second dichroic mirror, a first reflecting mirror and an IFM device; the nonlinear crystal is used to generate signal photons and idle photons in a forward or reverse spontaneous parametric down conversion process; the second dichroic mirror is used to reflect the idle photons into the IFM device; only when an object is placed in the IFM device, the idle photons generated in the forward spontaneous parametric down conversion process return to the nonlinear crystal, and partial path homogeneity is established on the induced coherence module to achieve induced coherence; the single-pixel imaging module is used to sense and reconstruct an object image through single counting of signal photons; the invention can effectively avoid direct interaction between illumination photons and objects, and can achieve interaction-free, single-pixel quantum imaging in far-infrared and terahertz bands.

Description

Technical Field

[0001] The present invention belongs to the field of quantum sensing and imaging technology, and in particular is a non-interaction, single-pixel quantum imaging system for undetected photons. Background Art

[0002] Using quantum technology, people have developed a variety of quantum imaging schemes, such as ghost imaging, interaction-free measurement (IFM), and quantum imaging of undetected photons (QIUP). These quantum imaging schemes help to improve imaging capabilities and expand the scope of imaging applications. The ghost imaging scheme relies on the spatial correlation characteristics of photon pairs and requires two-photon coincidence measurements. Inspired by ghost imaging, people have proposed computational ghost imaging schemes. Computational ghost imaging and single-pixel imaging are based on the same principle and do not require two-photon correlation, but rely on the correlation between single photons and programmable patterns. Single-pixel imaging can use spatial light modulators and single-pixel detectors to obtain spatial information of objects without the use of any detectors with spatial resolution, such as CCD cameras.

[0003] Quantum Imaging of Undetected Photons (QIUP) is a quantum imaging scheme developed based on the concept of induced coherence. The induced coherence interferometer consists of two entangled sources that can generate a pair of signal photons and idle photons. By overlapping the idle photon paths of the two entangled sources, we can establish path homogeneity, thereby removing the source information of the photon pair. The object is placed in the idle photon path. Using induced coherence, the object phase and transmittance information carried by the idle photons is transferred to the quantum interference of the signal photons. Unlike ghost imaging, quantum imaging of undetected photons (QIUP) does not require the detection of the photons illuminating the object, nor does it require any coincidence measurement. The detection photons can choose a wavelength completely different from the illumination photons. The former focuses on convenient detection, while the latter focuses on practical applications. This is a unique advantage of quantum imaging of undetected photons (QIUP). The concept of induced coherence has been applied to many fields such as biological microscopy imaging, mid-infrared imaging, terahertz sensing, infrared spectroscopy, holographic imaging, optical coherence tomography, and Fourier transform infrared spectroscopy.

[0004] Although ghost imaging, single-pixel imaging, and quantum imaging of undetected photons (QIUP) all have their own unique advantages, they cannot avoid direct interactions between photons and objects, which is particularly detrimental to the measurement and imaging of fragile samples such as biological tissues. Interaction-free measurement (IFM) can use the wave-particle duality of single photons to sense the presence of objects by observing changes in interference patterns. In interaction-free measurement (IFM), we can detect objects even if photons do not interact directly with objects. There are many different implementation schemes for interaction-free measurement (IFM), such as the Elitzur-Vaidman scheme and the quantum Zeno scheme. In addition, interaction-free measurement (IFM) can also be combined with ghost imaging to achieve interaction-free ghost imaging. However, due to the lack of long-wavelength single-photon detectors, interaction-free measurement (IFM) cannot be applied to infrared and terahertz bands. Imaging in the infrared and terahertz bands has very important applications in many fields, such as bioimaging, security testing, and material research. At present, the development of new quantum imaging technologies for application in material research and life sciences is a very important research topic. Summary of the invention

[0005] Purpose of the invention: To solve the problem that interaction-free measurement (IFM) cannot be applied to infrared and terahertz bands, the present invention proposes an interaction-free, single-pixel quantum imaging system and method for undetected photons based on interaction-free measurement, induced coherence and single-pixel imaging.

[0006] Technical solution: An interaction-free, single-pixel quantum imaging system for undetected photons, comprising a laser, a first dichroic mirror, a third dichroic mirror, an induced coherence module, and a single-pixel imaging module;

[0007] The laser is used to emit pump laser;

[0008] The first dichroic mirror is located between the laser and the induced coherence module, and is used to direct the pump laser to the induced coherence module, and to separate the laser and the photon pairs generated by the spontaneous parametric down-conversion process;

[0009] The third dichroic mirror is located between the first dichroic mirror and the single-pixel imaging module, and is used to transmit signal photons to the single-pixel imaging module and reflect and filter out idle photons;

[0010] The induced coherence module includes a nonlinear crystal, a second dichroic mirror, a first reflector and an IFM device; wherein,

[0011] The nonlinear crystal is used to generate signal photons and idle photons in a forward or reverse spontaneous parametric down conversion process;

[0012] The second dichroic mirror, located after the nonlinear crystal, is used to separate the idle photons and signal photons generated in the forward spontaneous parametric down-conversion process and reflect the idle photons into the IFM device;

[0013] The first reflector is located at the end of the transmission light path of the second dichroic mirror and is used to reflect the laser light and the signal photons back to the nonlinear crystal;

[0014] The IFM device comprises a beam splitter, a second reflector and a third reflector; the beam splitter is located in the reflection light path of the second dichroic mirror, and is used to split idle photons into two paths, a reflection path and a transmission path; the second reflector is located at the end of the reflection light path of the beam splitter, and is used to reflect idle photons back to the beam splitter; the third reflector is located at the end of the transmission light path of the beam splitter, and is used to reflect idle photons back to the beam splitter; the second reflector and the beam splitter form a path 2; the third reflector and the beam splitter form a path 3; only when the object is placed in the path 3, the idle photons generated in the forward spontaneous parametric down-conversion process return to the nonlinear crystal along the path 2 through the beam splitter and the second dichroic mirror, and establish partial path homogeneity on the induced coherence module;

[0015] The single-pixel imaging module is used to obtain spatial information of an imaged object, and includes a spatial light modulator and a single-photon detector without spatial resolution; wherein the spatial light modulator is used to display a sampling pattern, and the single-photon detector without spatial resolution is used to detect the number of single photons associated with the sampling pattern; based on the number of single photons associated with the sampling pattern, it is determined whether the object exists in the IFM device, and based on the number of single photons associated with the sampling pattern, a pixelated image of the object is reconstructed.

[0016] Furthermore, it also includes a first translation stage, a second translation stage and a third translation stage; used to adjust the relative optical delay between the signal photon, the idle photon and the pump laser;

[0017] The first translation stage is mounted on the first reflecting mirror and is used to adjust the phase of the signal photon.

[0018] The second translation stage is mounted on the second reflecting mirror and is used to adjust the phase of idle photons in the reflected light path of the beam splitter.

[0019] The third translation stage is mounted on the third reflecting mirror and is used to adjust the phase of idle photons in the transmission light path of the beam splitter.

[0020] Furthermore, the sampling pattern is a pattern constructed by a Hadamard matrix.

[0021] Furthermore, the reconstructing a pixelated image of the object based on the number of single photons associated with the sampling pattern specifically includes:

[0022] The number of correlated single photons of all sampled patterns is used to construct the Hadamard spectrum of the image;

[0023] By performing an inverse Hadamard transform on the Hadamard spectrum, a pixelated image of the object is reconstructed.

[0024] Furthermore, the single-pixel imaging module is replaced with an enhanced charge-coupled device for performing interaction-free quantum imaging of undetected photons.

[0025] The present invention also discloses a non-interaction quantum sensing method for undetected photons, comprising the following steps:

[0026] Constructing an interaction-free, single-pixel quantum imaging system for undetected photons;

[0027] Fix the IFM device at the interference cancellation point;

[0028] A histogram of signal photon single counts is obtained, and based on the histogram of signal photon single counts, it is determined whether there is an object in the IFM device. If the signal photon single count exceeds the counting interval of the threshold, there is an object in the IFM device; if the signal photon single count is lower than the counting interval of the threshold, there is no object in the IFM device.

[0029] The present invention also discloses a method for non-interaction quantum imaging of undetected photons, comprising the following steps:

[0030] Step 1: Build an interaction-free, single-pixel quantum imaging system for undetected photons;

[0031] Step 2: Fix the IFM device at the phase point (θ = π, φ = 0) and record the signal photon image under this phase setting;

[0032] Step 3: adjust the relative phase φ of the IFM device to π, adjust the phase θ of the signal photon to 0, and record the signal photon image under this phase setting;

[0033] Step 4: Subtract the signal photon image obtained in step 2 from the signal photon image obtained in step 3 to obtain the final imaging result.

[0034] The present invention also discloses a method for non-interaction, single-pixel quantum imaging of undetected photons, comprising the following steps:

[0035] Step 1: Build an interaction-free, single-pixel quantum imaging system for undetected photons;

[0036] Step 2: Under the four phase settings of (θ=0, φ=π), (θ=π, φ=π), (θ=π, φ=0) and (θ=0, φ=0), record the single photon counts associated with each sampling pattern, denoted as: C(θ=π, φ=0), C(θ=0, φ=0), C(θ=0, φ=π) and C(θ=π, φ=π);

[0037] Step 3: Based on C(θ=π, φ=0), C(θ=0, φ=0), C(θ=0, φ=π) and C(θ=π, φ=π), calculate the number of associated photons C of each sampling pattern M :

[0038] C M =C(θ=0,φ=π)-C(θ=π,φ=π)+C(θ=π,φ=0)-C(θ=0,φ=0) (11)

[0039] Step 4: Multiply each sampled pattern by the number of photons in its light link to obtain a set of weighted patterns;

[0040] Step 5: Add all weighted patterns to get the final imaging result

[0041] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0042] (1) The present invention utilizes the broadband matching condition of nonlinear crystals to flexibly select the wavelength of the correlated photon pair; the present invention utilizes low-noise, high-efficiency single-photon detectors to achieve non-interaction, single-pixel quantum imaging in the bands where there is a lack of efficient CCD cameras and single-photon detectors, such as the far-infrared (Far-IR) and terahertz (THz) bands;

[0043] (2) The imaging system of the present invention has potential application value in many fields, such as the study of fragile materials and life sciences;

[0044] (3) The imaging system of the present invention can avoid direct interaction between illumination photons and objects, thereby reducing damage and interference to the detected objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Conceptual diagram and schematic diagram of the non-interaction, single-pixel quantum imaging system for undetected photons;

[0046] Figure 2 Setup diagram for the non-interaction, single-pixel quantum imaging system for undetected photons;

[0047] Figure 3 Experimental results for a non-interacting quantum sensing system with undetected photons;

[0048] Figure 4 Design diagram for quantum imaging;

[0049] Figure 5 Imaging results of the non-interaction quantum imaging system for undetected photons;

[0050] Figure 6 is the Hadamard spectrum measurement result of the non-interacting, single-pixel quantum imaging system with undetected photons; Figure 6 (a)~ Figure 6 (c) Figure 6 (d)~ Figure 6 (e) in the figure are the Hadamard spectra of 256 and 1024 Hadamard sampling patterns respectively;

[0051] Figure 7 This is the image reconstruction result of the non-interaction, single-pixel quantum imaging system for undetected photons; Figure 7 (a) and Figure 7 (b) in the figure are the reconstructed images of 256 and 1024 Hadamard sampling patterns respectively. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is now further described in conjunction with the accompanying drawings.

[0053] The present invention discloses a non-interaction, single-pixel quantum imaging system with undetected photons, which is a new quantum imaging solution that can break through the constraints of typical imaging systems. Figure 1 As shown in (a) in the figure, a typical imaging system requires three elements. The first element is physical interaction, that is, the photons radiated by the light source hit the object and interact with the object; the second element is direct detection, that is, the scattered photons need to be directly detected to infer the existence of the object; the third element is a detector with spatial resolution, such as CCD, which is used to obtain the spatial information of the object.

[0054] like Figure 1 As shown in (b), the imaging system of the present invention completely breaks through the three elements of typical imaging, that is, it does not require direct interaction between photons and objects, and does not require direct detection of scattered photons and CCD cameras. In the bands where there is a lack of efficient CCD cameras and single-photon detectors, such as the far-infrared (Far-IR) and terahertz (THz) bands, the present invention uses visible light single-photon detectors for quantum imaging, while avoiding direct interaction between scattered photons and objects, reducing damage and interference to the detected objects.

[0055] like Figure 1As shown in (c) in the figure, the imaging system of the present invention combines three quantum and quantum-derived technologies: induced coherence, IFM interferometer, and single-pixel imaging. The detected object is placed in the IFM interferometer. Using the IFM interferometer, idle photons can achieve phase-free imaging. Two entangled sources Source-1 and Source-2 constitute an induced coherence interferometer. Using induced coherence, the image information of the object is transferred from idle photons to signal photons. Finally, using the single-pixel imaging method, the object image is reconstructed by single counting of signal photons.

[0056] Figure 2 The imaging system of the present invention mainly includes: a laser, a first dichroic mirror DM 1 、The third dichroic mirror DM 3 , induced coherence module IC and single pixel imaging module SPI. The first dichroic mirror DM 1 Located between the laser Laser and the induced coherence module IC, it is used to direct the pump laser to the induced coherence module and to separate the photon pairs generated by the laser and the spontaneous parametric down-conversion process; the third dichroic mirror DM 3 , located in the first dichroic mirror DM 1 and the single pixel imaging module SPI, used to transmit signal photons to the single pixel imaging module SPI and filter out idle photons; the induced coherence module IC is located between the first dichroic mirror DM 1 After that, the single pixel imaging module is located at the third dichroic mirror DM 3 after.

[0057] The induced coherence module IC of the present invention mainly comprises: a double-pass nonlinear crystal NC, a second dichroic mirror DM 2 , the first reflector R 1 and IFM device; nonlinear crystal NC, located in the first dichroic mirror DM 1 With the second dichroic mirror DM 2 Between; the second dichroic mirror DM 2 , located between the nonlinear crystal NC and the first reflector R 1 It is used to separate the idle photons and signal photons generated in the forward spontaneous parametric down-conversion process and reflect the idle photons into the IFM device; the first reflector R 1 , located in the second dichroic mirror DM 2 The end of the transmission light path is used to reflect the laser and signal photons back to the nonlinear crystal; the IFM device is located at the second dichroic mirror DM 2 Reflected light path.

[0058] The IFM device is implemented by a Michelson interferometer, including: a beam splitter BS, a second reflector R 2 and the third reflector R3 The beam splitter BS is located at the second dichroic mirror DM 2 and the second reflector R 2 / Third reflector R 3 The second reflector R 2 Located at the end of the beam splitter reflection light path, it is used to reflect idle photons back to the beam splitter; the third reflector R 3 Located at the end of the beam splitter transmission light path, it is used to reflect idle photons back to the beam splitter. The pump laser emitted by the laser Laser transmits the double-pass nonlinear crystal NC twice, and generates a pair of correlated photons through the forward (from left to right) or reverse (from right to left) spontaneous parametric down-conversion process (SPDC). The optical link photons are signal photons and idle photons. The present invention utilizes the broadband matching conditions of the nonlinear crystal to flexibly select the wavelength of the correlated photon pair. The idle photons generated by the forward SPDC process are passed through the second dichroic mirror DM 2 When the relative phase φ of the IFM device is set to 0 and there is no object in the IFM device, the idle photons generated by the forward SPDC process cannot return to the nonlinear crystal, so the induced interference is suppressed; in this case, the interference between the idle photons and the signal photons cannot be observed. If an object is placed in path 3 of the IFM device, path 3 is the path of the third reflector R. 3 The idle photons generated by the forward SPDC process can be reflected twice by the beam splitter BS along path 2 and return to the double-pass nonlinear crystal NC. Path 2 is formed by the second reflector R 2 and the beam splitter BS; then the partial path homogeneity is established on the induced coherence interferometer. Therefore, by observing the interference pattern of the signal photons, the existence of the object can be inferred.

[0059] In this embodiment, by first reflecting mirror R 1 , the second reflector R 2 , the third reflector R 3 The first displacement stage is installed on the first reflector to adjust the phase of the signal photon. The second displacement stage is installed on the second reflector to adjust the phase of the idle photon in the reflected light path of the beam splitter. The third displacement stage is installed on the third reflector to adjust the phase of the idle photon in the transmitted light path of the beam splitter. The relative optical delay between the signal photon, the idle photon and the pump laser can be adjusted by the electric displacement stage to establish the path homogeneity of the forward and reverse SPDC processes, and finally achieve induced interference.

[0060] It should be emphasized that during the entire imaging process, the idle photons do not interact directly with the object. The subtlety of the IFM device of the present invention lies in the use of the wave-particle duality of single photons. Since a single photon has particle properties, it cannot be split into two on the BS. Therefore, the idle photons returning to the nonlinear crystal must not pass through path 3, that is, they do not interact directly with the object.

[0061] The single pixel imaging module SPI of the present invention is used to obtain the spatial information of the imaging object, see Figure 2 In (a), the single-pixel imaging module SPI is mainly composed of two parts: a spatial light modulator SLM and a single-photon detector SPD without spatial resolution; the spatial light modulator SLM is used to display the sampling pattern, and the single-photon detector SPD without spatial resolution is used to detect the number of single photons associated with the sampling pattern. In the experiment, a Hadamard pattern can be selected as the sampling pattern. The number of single photons of all sampling patterns constitutes the Hadamard spectrum of the image. By performing a Hadamard inverse transform on the Hadamard spectrum, a pixelated image of the object can be reconstructed. The present invention utilizes a low-noise, high-efficiency single-photon detector so that the quantum imaging system can be applied to non-interaction, single-pixel quantum imaging in the Far-IR or THz bands in the future.

[0062] The present invention can also use an enhanced charge coupled device ICCD as a detection device, that is, an enhanced charge coupled device ICCD is used to replace the single pixel imaging module SPI for imaging, such as Figure 2 As shown in (b), an enhanced charge-coupled device (ICCD) is used to achieve interaction-free quantum imaging of undetected photons.

[0063] The technical solution of the present invention is now further described in conjunction with the accompanying drawings and embodiments.

[0064] Embodiment 1:

[0065] The experiment of non-interaction quantum sensing of undetected photons is now used to illustrate that the quantum imaging system of the present invention can realize non-interaction quantum sensing of undetected photons of opaque objects.

[0066] First, the IFM device is fixed at the interference cancellation point (φ = 0). Considering factors such as the imperfect IFM interference contrast and optical path calibration, there is residual interference in the signal photons, such as Figure 3 As shown in (a) in the figure, the contrast of the residual interference is 11.3±1.9%. Ideally, the interference contrast of the signal photon should be 0. If an opaque object is placed in path 3 of the IFM device, the idle photons generated by the forward SPDC process will not interact directly with the object, but will be reflected back to the double-pass nonlinear crystal NC through path 2. Figure 3As shown in (b), the idle photons without interaction will induce interference with the signal photons, and the interference contrast is 22.3±1.8%. Therefore, the presence or absence of an object determines the different interference contrasts of the signal photons. In the experimental operation, the maximum count of induced interference ( Figure 3 The dashed line in (b) indicates that IFM is successfully implemented, and the average count of residual interference ( Figure 3 The dashed line in (a) indicates that the object does not exist. Under the condition of no direct interaction with the object, this embodiment determines whether the object exists in the IFM device by single counting of signal photons.

[0067] In the non-interaction quantum sensing experiment without detecting photons, the histograms of the signal photon single counts are obtained when the object is present (light gray, left histogram) and not present (dark gray, right histogram), as shown in Figure 2. Figure 3 The existence of an object can be determined by Figure 3 (c) and Figure 3 The critical threshold judgment shown by the black dashed line in (d) is about 3.4σ away from the average value of the signal single photon count (when the object exists and does not exist). Figure 3 (c) and Figure 3 As shown in (d) in the figure, the existence (count interval exceeding the threshold) and non-existence (count interval below the threshold) of the object can be clearly distinguished, with a confidence level exceeding 99.93%.

[0068] Embodiment 2:

[0069] The quantum imaging experiment without interaction of detected photons is now used to illustrate that the quantum imaging system of the present invention can obtain an image of an object with a high signal-to-noise ratio.

[0070] This embodiment adopts Figure 2 The intensified charge-coupled device (ICCD) shown in (b) is used as a detection device to achieve interaction-free quantum imaging of undetected photons.

[0071] Now we use 3D printed 'NJU' logo as the image, Figure 4 As shown, the image includes character area Zone II and other area Zone I. The character area Zone II is transparent, and other area Zone I is opaque. The image has a certain spatial structure. If the image is placed in the path 3 of the IFM device, other area Zone I and character area Zone II have different signal photon counts and interference contrast:

[0072] Through theoretical analysis, the interference patterns of other areas Zone I and character area Zone II can be calculated:

[0073]

[0074]

[0075] Where P I(x,y) and P II(x,y) They represent the signal photon yields of other zones, Zone I and Zone II, respectively, which are related to the pump laser and the NC parameters of the double-pass nonlinear crystal. θ represents the phase of the signal photon, φ represents the relative phase of the idle photon in the IFM, and (x, y) represents the spatial position of the down-converter photon.

[0076] At the constructive interference point (φ=π), the complete interference pattern of the signal photon can be described as:

[0077]

[0078] By adjusting the phase θ, the interference constructive diagram C is obtained. max (θ, φ=π) and interference destructive diagram C min (θ, φ=π):

[0079]

[0080]

[0081] At the interference cancellation point (φ=0), the complete interference pattern of the signal photon can be described as:

[0082]

[0083] In this case, the constructive interference pattern C max (θ, φ=0) and the cancellation graph C min (θ, φ=0) are:

[0084]

[0085]

[0086] In order to improve the imaging contrast, subtract formula (4) from formula (7) to obtain the following image:

[0087] C max (θ,φ=π)-C max (θ,φ=0)=P II(x,y) (9)

[0088] Ideally, only the character zone Zone II has signal photon counts, and the other zone Zone I has no counts.

[0089] This data processing approach is employed in non-interaction quantum imaging experiments with undetected photons.

[0090] In the experiment, it is necessary to record the signal photon images under two different phase settings, namely (θ=0, φ=π) and (θ=π, φ=0). Including:

[0091] First, the IFM device is fixed at the phase point (θ = π, φ = 0). This phase setting is consistent with the phase setting used in the non-interaction quantum sensing experiment of undetected photons in Example 1. Under this phase setting, the first image of the 'NJU' logo is recorded, as shown in FIG. Figure 5 As shown in (b) in .

[0092] Then, the relative phase φ of the IFM device is adjusted to π, and the phase θ of the signal photon is adjusted to 0, that is, (θ=0, φ=π). Under this phase setting, if the object does not exist, the idle photons generated by the forward SPDC process will decisively return to the double-pass nonlinear crystal NC. Therefore, the signal photons associated with the idle photons in the character area ZoneII interfere constructively. Under the phase setting of (θ=0, φ=π), the imaging image of the 'NJU' logo is recorded, as shown in Figure 5 As shown in (a) in .

[0093] In order to enhance the signal-to-noise ratio of the interference image, the images acquired under the above two phase settings are subtracted to obtain the final imaging result of the 'NJU' logo, as shown in Figure 5 As shown in (c) in FIG. 1 , it can be seen that through the above data processing, an object image with a high signal-to-noise ratio can be obtained.

[0094] Embodiment 3:

[0095] The non-interaction, single-pixel quantum imaging experiment of undetected photons is now used to illustrate that the quantum imaging system of the present invention can achieve the reconstruction of the image of the object.

[0096] This embodiment adopts Figure 2 The single-pixel imaging module shown in (a) realizes interaction-free, single-pixel quantum imaging of undetected photons.

[0097] Now we use 3D printed 'NJU' logo as the image, Figure 4 As shown, the imaging image includes a character area Zone II and other areas Zone I, the character area Zone II is transparent, and other areas Zone I are opaque.

[0098] If the imaging pattern is placed in path 3 of the IFM device, the signal photon counts in two different areas will have different interference contrasts. Through theoretical analysis, the interference patterns of other areas Zone I and character area Zone II can be calculated:

[0099]

[0100]

[0101] Where P I(x,y) and P II(x,y) They represent the signal photon yields of other zones, Zone I and Zone II, respectively, which are related to the pump laser and the NC parameters of the double-pass nonlinear crystal. θ represents the phase of the signal photon, φ represents the relative phase of the idle photon in the IFM, and (x, y) represents the spatial position of the down-converter photon.

[0102] At the constructive interference point (φ=π), the complete interference pattern of the signal photon can be described as:

[0103]

[0104] By adjusting the phase θ, the interference constructive diagram C is obtained. max (θ, φ=π) and interference destructive diagram C min (θ, φ=π):

[0105]

[0106]

[0107] At the interference cancellation point (φ=0), the complete interference pattern of the signal photon can be described as:

[0108]

[0109] Constructive interference diagram C max (θ, φ=0) and the cancellation graph C min (θ, φ=0) are:

[0110]

[0111]

[0112] For non-interaction, single-pixel quantum imaging experiments with undetected photons, the following method is used to process the imaging data:

[0113] C max (θ,φ=π)-C min (θ,φ=π)-C max (θ,φ=0)+C min (θ,φ=0)=2P II(x,y) (10)

[0114] The pixel size of the Hadamard pattern of this embodiment is selected as 64×64. A small number of sampling patterns (256) are first used to verify the feasibility of the imaging system of this embodiment, and then the number of sampling patterns is increased (1024) to obtain a higher resolution image. The two sampling patterns account for 6.25% and 25% of the total number of pixels respectively.

[0115] The single photon counts associated with each Hadamard pattern were recorded under four phase settings: C(θ=π, φ=0), C(θ=0, φ=00, C(θ=0, φ=π) and C(θ=π, φ=π). That is, the single photon counts under the four settings of (θ=0, φ=π), (θ=π, φ=π), (θ=π, φ=0) and (θ=0, φ=0).

[0116] Since the photon count obtained by formula (10) is twice that of formula (9), the data processing method shown in formula (10) can significantly enhance the image brightness. According to the above four single photon counts, based on formula (10), the final associated photon number C of each Hadamard pattern is calculated M :

[0117] C M =C(θ=0,θ=π)-C(θ=π,φ=π)+C(θ=π,φ=0)-C(θ=0,φ=0) (11)

[0118] Each Hadamard pattern in the sampled set is then multiplied by the corresponding number of associated photons to obtain a set of weighted patterns.

[0119] Finally, all weighted patterns are added together to achieve the reconstruction of the object image. The above image reconstruction algorithm is equivalent to performing Hadamard inverse transform on the Hadamard spectrum.

[0120] The measured Hadamard spectrum is as follows Figure 6 By performing Hadamard inverse transformation on the Hadamard spectrum, the image of the 'NJU' logo is reconstructed, as shown in Figure 7 shown.

[0121] During the entire imaging process, neither the idle photons nor the signal photons interact directly with the object, and no CCD camera of any wavelength is required for detection. Only visible light single-photon detectors are used to achieve non-interaction, single-pixel quantum imaging in the near-infrared band.

Claims

1. An interaction-free, single-pixel quantum imaging system for undetected photons, characterized in that: It includes a laser, a first dichroic mirror, a third dichroic mirror, an induced coherence module and a single pixel imaging module; The laser is used to emit laser light; The first dichroic mirror is located between the laser and the induced coherence module, and is used to direct the laser light toward the induced coherence module, and to separate the idle photons and signal photons generated by the laser light and the spontaneous parametric down-conversion process; The third dichroic mirror is located between the first dichroic mirror and the single-pixel imaging module, and is used to transmit signal photons to the single-pixel imaging module and reflect and filter out idle photons; The induced coherence module includes a nonlinear crystal, a second dichroic mirror, a first reflector and an IFM device; wherein, The nonlinear crystal is used to generate signal photons and idle photons in a forward spontaneous parametric down conversion process; The second dichroic mirror, located after the nonlinear crystal, is used to separate the idle photons and signal photons generated in the forward spontaneous parametric down-conversion process and reflect the idle photons into the IFM device; The first reflector is located at the end of the transmission light path of the second dichroic mirror and is used to reflect the laser light and the signal photons back to the nonlinear crystal; The IFM device comprises a beam splitter, a second reflector and a third reflector; the beam splitter is located in the reflection light path of the second dichroic mirror, and is used to split idle photons into two paths, a reflection path and a transmission path; the second reflector is located at the end of the reflection light path of the beam splitter, and is used to reflect idle photons back to the beam splitter; the third reflector is located at the end of the transmission light path of the beam splitter, and is used to reflect idle photons back to the beam splitter; the second reflector and the beam splitter form a path 2; the third reflector and the beam splitter form a path 3; only when the object is placed in the path 3, the idle photons generated in the forward spontaneous parametric down-conversion process return to the nonlinear crystal along the path 2 through the beam splitter and the second dichroic mirror, and establish partial path homogeneity on the induced coherence module; The single-pixel imaging module is used to obtain spatial information of an imaged object, and includes a spatial light modulator and a single-photon detector without spatial resolution; wherein the spatial light modulator is used to display a sampling pattern, and the single-photon detector without spatial resolution is used to detect the number of single photons associated with the sampling pattern; based on the number of single photons associated with the sampling pattern, it is determined whether the object exists in the IFM device, and based on the number of single photons associated with the sampling pattern, a pixelated image of the object is reconstructed.

2. The non-interaction, single-pixel quantum imaging system of undetected photons according to claim 1, characterized in that: It also includes a first translation stage, a second translation stage and a third translation stage, which are used to adjust the relative optical delay between the signal photon, the idle photon and the pump laser; The first translation stage is mounted on the first reflecting mirror and is used to adjust the phase of the signal photon; The second translation stage is mounted on the second reflector and is used to adjust the phase of idle photons in the reflected light path of the beam splitter; The third translation stage is mounted on the third reflecting mirror and is used to adjust the phase of idle photons in the transmission light path of the beam splitter.

3. The non-interaction, single-pixel quantum imaging system of undetected photons according to claim 1, characterized in that: The sampling pattern is a pattern constructed by a Hadamard matrix.

4. The non-interaction, single-pixel quantum imaging system of undetected photons according to claim 3, characterized in that: The reconstructing a pixelated image of the object based on the number of single photons associated with the sampling pattern specifically includes: The number of correlated single photons of all sampled patterns is used to construct the Hadamard spectrum of the image; By performing an inverse Hadamard transform on the Hadamard spectrum, a pixelated image of the object is reconstructed.

5. The non-interaction, single-pixel quantum imaging system of undetected photons according to claim 1, characterized in that: The single pixel imaging module is replaced with an enhanced charge coupled device for interaction-free quantum imaging of undetected photons.

6. A method for non-interaction quantum sensing of undetected photons, characterized in that: The following steps are involved: Constructing an interaction-free, single-pixel quantum imaging system for undetected photons as described in any one of claims 1 to 4; Fix the IFM device at the interference cancellation point; A histogram of signal photon single counts is obtained, and based on the histogram of signal photon single counts, it is determined whether there is an object in the IFM device. If the signal photon single count exceeds the counting interval of the threshold, there is an object in the IFM device; if the signal photon single count is lower than the counting interval of the threshold, there is no object in the IFM device.

7. A method for non-interaction quantum imaging of undetected photons, characterized in that: The following steps are involved: Step 1: constructing an interaction-free, single-pixel quantum imaging system for undetected photons as described in claim 5; Step 2: Fix the IFM device at the phase point (θ = π, φ = 0) and record the signal photon image under this phase setting; Step 3: adjust the relative phase φ of the IFM device to π, adjust the phase θ of the signal photon to 0, and record the signal photon image under this phase setting; Step 4: Subtract the signal photon image obtained in step 2 from the signal photon image obtained in step 3 to obtain the final imaging result.

8. A method for non-interaction, single-pixel quantum imaging of undetected photons, characterized by: The following steps are involved: Step 1: constructing an interaction-free, single-pixel quantum imaging system for undetected photons as described in claim 4; Step 2: Under the four phase settings of (θ=0, φ=π), (θ=π, φ=π), (θ=π, φ=0) and (θ=0, φ=0), record the single photon counts associated with each sampling pattern, denoted as: C(θ=π, φ=0), C(θ=0, φ=0), C(θ=0, φ=π) and C(θ=π, φ=π); Step 3: Based on C(θ=π, φ=0), C(θ=0, φ=0), C(θ=0, φ=π) and C(θ=π, φ=π), calculate the number of associated photons C of each sampling pattern M : C M =C(θ=0,φ=π)-C(θ=π,φ=π)+C(θ=π,φ=0)-C(θ=0,φ=0) (11) Step 4: Multiply each sampled pattern by the number of photons in its light link to obtain a set of weighted patterns; Step 5: Add all weighted patterns to obtain the final imaging result.

Images