Device and method for characterizing the spectral phase of at least one single photon of a signal

Abstract

The invention relates to a device (1) for characterizing the spectral phase of at least one single photon of a signal (5), comprising a first light source (2) for generating at least one pump pulse (3) with a pump pulse spectrum, a supply line (4') for a second light source (4) for supplying at least one signal pulse (5) with a signal pulse spectrum, a pulse shaper (6) for shaping the pump pulse (3) in such a way that two phase-different spectral frequency bins (12) of the pump pulse (3) are transmitted with an adjustable frequency, a mixing device (7) for mixing the shaped pump pulse (3) with the signal pulse (5) and outputting at least one first part (8) of the signal pulse spectrum, with the first part (8) comprising an overlap (11) of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse (3), a measuring unit (9) for measuring the intensity of the first part (8) of the signal pulse spectrum and coding a second part of the signal pulse spectrum, with the second part comprising the overlap (11) of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum, and an evaluation unit (10) for reconstructing at least one phase and / or one coherence property of the signal pulse (5). In this way, a simple, fast and reliable characterization of the spectral phase and coherence properties of at least one single photon light pulse is made possible.

Description

[0001] Device and method for characterizing the spectral phase of at least one single photon of a signal

[0002] The present invention relates generally to the field of quantum optical measurement technology, in particular to techniques for characterizing the spectral phase and coherence properties of light pulses down to the single-photon level.

[0003] Classical pulse characterization techniques, such as SPIDER (Spectral Phase Interferometry for Direct Electric-Field Reconstruction) or FROG (Frequency-Resolved Optical Gating), have long been established and provide reliable information about the spectral phase and amplitude of ultrashort light pulses. However, both methods rely on nonlinear optical processes with high intensities and therefore require a sufficient number of photons to generate a measurable interaction. This requirement is not met for single-photon light pulses, rendering classical methods inapplicable in this regime.

[0004] To address the field of quantum optics, various alternative approaches have been developed. These include, for example, electro-optical methods, such as an electro-optical variant of SPIDER (electro-optical shearing interferometry; EOSI), as well as methods for complete state tomography of single photons. Spectrally resolved interference of two photons has also been used to determine the spectral phase of single-photon light pulses by interfering an unknown pulse with a time-delayed reference pulse. These methods are conditionally compatible with single photons, requiring either highly complex modulation schemes, very laborious data acquisition, or a well-characterized reference pulse.

[0005] All known approaches share certain limitations: either they are technically very complex and therefore difficult to implement in experimental or even integrated platforms, or they require a known reference pulse. Furthermore, they often presuppose fully coherent light pulses, which is generally not the case, especially with single-photon pulses. In addition, spectral resolution is frequently required, which increases the measurement time and degrades the signal-to-noise ratio. Finally, many methods are limited to the characterization of a single unknown pulse, whereas in realistic scenarios, the simultaneous analysis of multiple unknown pulses is desirable.

[0006] Based on this, the object of the present invention is to provide a method and a device that enable a simple, fast and reliable characterization of the spectral phase and coherence properties of at least one single-photon light pulse, with particular emphasis on compatibility with the single-photon level and a reduction in measurement complexity.

[0007] This task is solved by the subject matter of the independent claims. Further details are found in the dependent claims.

[0008] According to the invention, a device for characterizing the spectral phase of at least one single photon of a signal is provided, comprising a first light source for generating at least one pump pulse with a pump pulse spectrum, a feed line for a second light source for feeding at least one signal pulse with a signal pulse spectrum, a pulse shaper for shaping the pump pulse such that two phase-different spectral frequency bins of the pump pulse are forwarded at an adjustable frequency, a mixing device for mixing the shaped pump pulse with the signal pulse and outputting at least a first part of the signal pulse spectrum, wherein the first part comprises an overlap of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse, and a measuring unit for measuring the intensity of the first part of the signal pulse spectrum and encoding a second part of the signal spectrum.wherein the second part comprises the overlap of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum,

[0009] Evaluation unit for reconstructing at least one phase and / or one coherence property of the signal pulse. One aspect of the present invention therefore relates to a device for characterizing the spectral phase of at least one single photon of a signal.

[0010] Characterization refers in particular to the acquisition of information about physical properties, especially about a spectral phase. A spectral phase is a frequency-dependent phase shift of a light pulse that determines its temporal evolution and coherence properties. A single photon can be understood as a quantized photon of light detected at a level where the average number of photons per pulse is at most one. In the context of the invention, a signal is preferably an optical pulse carrying the phase to be characterized.

[0011] The device comprises a first light source for generating at least one pump pulse with a pump pulse spectrum. A light source is a device that emits coherent or partially coherent electromagnetic radiation in the form of ultrashort pulses. A pump pulse is a light pulse provided by the first light source, which serves as a reference and is characterized in the frequency domain by a pump pulse spectrum. An advantage of this is that by providing a controlled pump pulse, a defined baseline for comparison with a signal is created, thus enabling reliable and reproducible phase characterization.

[0012] Furthermore, the device is provided with a feed line for a second light source to supply at least one signal pulse with a signal pulse spectrum. A feed line is a transmission device that carries optical pulses from a source to a measuring unit. A signal pulse is a light pulse whose phase is unknown and which is described by a signal pulse spectrum. An advantage of this is that the separate supply of the signal pulse achieves a clean spatial and temporal separation of the pump and signal paths, enabling flexible and targeted analysis.

[0013] The device is designed to include a pulse shaper for shaping the pump pulse such that two phase-different spectral frequency bins of the pump pulse are forwarded at an adjustable frequency. A pulse shaper is an optical component that selectively modifies the spectral properties of a pulse. A frequency bin is a selected sub-range of the spectrum with a defined frequency position and bandwidth. An advantage of this is that by selecting two phase-different frequency bins, the spectral structure of the pump pulse is adapted so that interference effects between different spectral ranges can be investigated in a controlled manner, thereby achieving a more precise extraction of phase information.

[0014] The pulse shaper can be configured as a spatial light modulator, an acousto-optic modulator, or a phase-modulating liquid crystal modulator. A spatial light modulator (SLM) modifies the phase or amplitude distribution of light across a pixel array, an acousto-optic modulator (AOM) uses acoustic waves to modulate the frequency and intensity of a light beam, and a phase-modulating liquid crystal modulator allows for the precise control of the phase through electrically aligned liquid crystal layers. These different configurations enable the pulse shaper to flexibly structure the spectrum of the pump pulse and provide frequency bins with definable phases and variable spacing, thus allowing the measurement to be adapted to the characteristics of the signal.

[0015] According to the invention, the device comprises a mixing device for mixing the shaped pump pulse with the signal pulse and outputs at least a first part of the signal pulse spectrum, wherein the first part comprises an overlap of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse. In the present context, a mixing device is understood to be, in particular, a device designed to mix the shaped pump pulse with the signal pulse. For this purpose, a time-variable frequency beam splitter is suitable, for example, wherein the variability and frequency are adjustable by external control. The frequency beam splitter selects a single electromagnetic field mode according to its variable properties. An overlap is a common frequency range in which the signal and pump pulses are simultaneously present and can interfere.One advantage of this is that the interference in the overlap region converts the phase of the signal pulse into measurable intensity changes, thus enabling direct reconstruction without spectral resolution.

[0016] The overlap is, in particular, the shared frequency and time range in which the signal and pump pulses are simultaneously present and can interfere within the mixing device. It constitutes the physical basis for intensity measurement. Measuring the integrated intensity in this overlap range allows the relative phase information between the two pulses to be translated into measurable quantities. Thus, the overlap forms the bridge between the spectral phase, which cannot be measured directly, and the detectable intensities, making subsequent phase reconstruction technically feasible.

[0017] Furthermore, the device is designed to include a measuring unit for measuring the intensity of the first part of the signal pulse spectrum and for encoding a second part of the signal pulse spectrum, wherein the second part comprises the overlap of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum. A measuring unit is a detector arrangement that detects the intensities of optical signals and converts them into electrical signals. An offset is a shift of the spectrum by a defined frequency difference. An advantage of this is that the simultaneous acquisition of multiple overlap regions provides access to different spectral correlations of the signal pulse, thereby enabling a complete description of the spectral phase with fewer measurements and allowing for faster characterization.

[0018] The measuring unit comprises, in particular, at least one single-photon detector, preferably a superconducting nanowire single-photon detector (SNSPD) or an avalanche photodiode (APD). An SNSPD is characterized by high quantum efficiency, low dark count rates, and excellent temporal resolution, while an APD offers a compact and proven solution for single-photon counting. Both detector types enable reliable intensity measurements even at extremely weak signals. This makes the device usable for operation at the single-photon level, thus technically solving the problem of obtaining phase information in the quantum realm.

[0019] Finally, the device is designed to include an evaluation unit for reconstructing at least one phase and / or a coherence property of the signal pulse. An evaluation unit is a system for processing the data provided by the measurement unit, typically in the form of computer-aided signal processing. A coherence property describes the signal's ability to maintain interference phenomena across different frequency components. An advantage of this is that the reconstruction not only determines a single spectral phase but also characterizes the pulse's coherence, thus allowing for a better assessment of the pulse's suitability for applications in quantum optics.

[0020] It is therefore a key aspect of the invention that the characterization of the spectral phase and / or coherence properties of at least one single-photon light pulse is carried out by evaluating intensities in defined overlap regions, without requiring a spectral resolution or a known reference pulse.

[0021] According to a further development of the invention, the relative phase between the two phase-dissimilar frequency bins of the pump pulse is variably adjustable. A relative phase can be understood as the phase difference between two spectral components of a pulse that occupy different frequency positions. Frequency bins are selected sub-regions of the spectrum, each covering a narrow frequency bandwidth. An advantage of this is that different interference situations can be selectively generated by adjusting the relative phase, resulting in a wider range of measurement data. This makes the reconstruction of the spectral phase more reliable and robust against noise, since varying the relative phase allows for improved information density.

[0022] According to a further development of the invention, the frequency spacing of the frequency bins of the pump pulse is variably adjustable. A frequency spacing is the difference between the center frequencies of two selected spectral ranges. An advantage of this is that adjusting the spacing makes different spectral regions of the signal pulse accessible, allowing the measurement to be flexibly adapted to various spectral structures. This enables finer sampling of the spectral phase and contributes to improved reconstruction accuracy, as a person skilled in the art can adjust the spectral bandwidth of the analysis to the characteristics of the signal by changing the spacing. According to a further development of the invention, the measuring unit is designed to simultaneously acquire the intensities of several outputs of the mixing device.An output can be understood as a channel in which the optical signals generated by the mixing device are present separately. Parallel acquisition means that the measurement is performed simultaneously in all channels. One advantage of this is that parallel acquisition reduces the measurement time and allows multiple overlapping regions to be analyzed at the same time. This increases the efficiency of the characterization and reduces the need for repeated individual measurements, thus enabling faster and more reliable phase reconstruction.

[0023] According to a further development of the invention, the mixing device for mixing the shaped pump pulse with the signal pulse comprises a quantum pulse gate. A quantum pulse gate is understood here, in particular, as a nonlinear optical component that couples two light pulses together and thereby generates new spectral components. The quantum pulse gate is preferably based on a nonlinear optical effect, in particular cross-phase modulation or sum-difference frequency generation. In cross-phase modulation, one pulse influences the phase of another through the nonlinear refractive index change of the medium, while in sum- or difference-frequency generation, new frequency components are created that are composed of the combination of the pulse spectra involved. Both mechanisms allow for coherent coupling of the pump and signal pulses and thus ensure that the spectral overlap regions are converted into measurable outputs.

[0024] According to a further development of the invention, the quantum pulse gate is designed with optimized dispersion properties to minimize spectral distortions. By selecting a suitable nonlinear optical effect, the quantum pulse gate can be designed such that the dispersion properties and the interaction efficiency are optimally adapted to the requirements of single-photon characterization. Dispersion properties are the dependence of the propagation speed of a pulse on its frequency. An advantage of this is that by adapting the dispersion in the quantum pulse gate, undesired spectral distortions are reduced, leading to more precise interference. This results in more accurate intensity measurement in the overlap region, enabling the phase and coherence properties of the signal pulse to be reconstructed with higher accuracy.

[0025] According to a further development of the invention, the evaluation unit is designed to reconstruct at least one phase of the pump pulse, taking the reconstructed signal pulse into account. An evaluation unit is a data processing unit that mathematically evaluates the intensities acquired by the measuring unit. Taking the reconstructed signal pulse into account means that its previously determined phase is included in the calculation as reference information. An advantage of this is that not only the phase of the signal pulse but also the phase of the pump pulse becomes available. This significantly expands the application possibilities, as both pulses involved can be described independently of each other. This convincingly fulfills the objective of achieving the most comprehensive characterization possible in the single-photon range.

[0026] According to the invention, a method for characterizing the phase of at least one single photon of a signal is further provided with the device described above, comprising the following method steps:

[0027] 51 Providing a pump pulse,

[0028] 52 Providing a signal pulse,

[0029] 53 forms of the pump pulse such that two phase-different spectral frequency bins of the pump pulse are provided with an adjustable frequency,

[0030] 54 Mixing the shaped pump pulse with the signal pulse,

[0031] 55 Outputting at least a first part of the signal pulse spectrum, wherein the first part comprises an overlap of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse,

[0032] 56 Measuring the intensity of the first part,

[0033] 57 Encoding a second part of the signal spectrum, wherein the second part comprises the overlap of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum, 58 Repeating steps S1 to S7 for different relative phases and / or frequency intervals between the spectral frequency bins,

[0034] 59 Reconstructing the phase and / or coherence properties of the signal pulse, taking into account the phase of the pump pulse.

[0035] Characterization means determining physical properties, in particular the spectral phase. A single photon is a quantized photon of light that exists at a level where the average number of photons per pulse is at most one. A signal is a light pulse that carries this phase and is described by its spectral distribution.

[0036] The plan is to first provide a pump pulse. A pump pulse is an optical pulse generated by a light source, serving as a controlled reference signal and characterized by its spectrum. One advantage of this is that a defined reference pulse is available, which serves as the basis for interference with the signal, thus enabling subsequent reconstruction.

[0037] For this purpose, a signal pulse is provided. A signal pulse is a light pulse with an unknown spectral phase, which is described by a signal pulse spectrum. One advantage of this is that this specific pulse is to be analyzed, so that its defined application ensures comparability with the pump pulse and enables reproducible measurement.

[0038] According to the invention, the pump pulse is shaped to provide two phase-different spectral frequency bins with an adjustable frequency. A frequency bin is a selected section of the spectrum with a defined center frequency and bandwidth. An advantage of this is that the targeted shaping of the pump pulse makes interference between different spectral ranges controllable, resulting in increased information density for subsequent analysis.

[0039] The shaped pump pulse is intended to be mixed with the signal pulse. Mixing refers to the coupling of two optical pulses in a nonlinear optical process, where shared frequency components form a new output state. One advantage of this is that the interaction of both pulses in the overlap region converts the phase information into measurable intensities.

[0040] The system provides for the output of at least a first part of the signal pulse spectrum, where this first part includes an overlap of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse. An overlap is the common frequency range in which the pump pulse and signal pulse are simultaneously present. An advantage of this is that the interference provides information about the phase of the signal pulse precisely in this range, thus eliminating the need for spectral resolution. The intensity of this first part is measured. Intensity is defined as the optical power per unit area in the selected spectral range. An advantage of this is that a pure intensity measurement is technically simpler to implement and can be performed with high sensitivity in the single-photon range.

[0041] The plan involves encoding a second part of the signal pulse spectrum, which comprises the overlap of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum. An offset is a shift of the spectrum by a defined frequency difference. One advantage of this is that analyzing such offsets reveals various spectral correlations, thus enabling a more complete characterization of the signal pulse.

[0042] The steps of provisioning, shaping, mixing, outputting, measuring, and encoding are intended to be repeated for different relative phases and / or frequency spacings between the spectral frequency bins. A relative phase is the difference in the temporal phase of two frequency components, while the frequency spacing describes the difference in their center frequencies. An advantage of this is that varying these parameters generates a wide range of interference patterns, thereby increasing the accuracy and robustness of the reconstruction.

[0043] Finally, the phase and / or coherence properties of the signal pulse are to be reconstructed taking into account the phase of the pump pulse. Coherence properties are the ability of a pulse to maintain interference across different frequencies. An advantage of this is that both the phase and the coherence can be described, which increases the explanatory power of the characterization and significantly expands the application possibilities in quantum optics.

[0044] The phase and coherence of the signal pulse can be derived from the overlap because the measured intensity depends directly on the spectral interference between the pump pulse and the signal pulse. The overlap describes the common frequency range in which both pulses are present simultaneously and interact within the mixing device. If the pump pulse is decomposed by the pulse shaper into two frequency bins with an adjustable phase difference, these defined spectral ranges couple with the corresponding components of the signal pulse. Varying the phase difference of the frequency bins changes the interference state in the overlap, and the measuring unit registers a change in intensity that depends on the relative phase of the signal pulse. In this way, the phase of the signal pulse can be reconstructed from the intensity oscillations.

[0045] The coherence of the signal pulse is determined by the contrast between these oscillations. With complete coherence, the intensities exhibit a clear sinusoidal relationship with high contrast. Partial coherence reduces the visibility of the oscillations because the interference is no longer perfectly stable. The spectral coherence function of the signal pulse can be determined by quantitative analysis of this contrast. By additionally varying the frequency spacing of the bins, the entire spectral range of the signal becomes accessible, allowing phase and coherence to be characterized across the entire spectrum. In this way, the signal pulse can be described solely through intensity measurements in the overlapping regions, without requiring spectral resolution.

[0046] According to a further development of the invention, step S8 provides for the continuous variation of the relative phase and / or the frequency spacing of the frequency bins. A relative phase can be understood as the temporal phase difference between two spectral ranges of a pulse. Continuous variation means that the phase is changed steplessly over a range of values. An advantage of this is that continuous variation enables finer sampling of the interference patterns, thereby increasing the accuracy of the phase reconstruction. It is evident to a person skilled in the art that the continuous adjustment of the relative phase increases the amount of information and thus allows for a more robust determination of the spectral properties of the signal pulse. A frequency spacing denotes the difference in the center frequencies of two selected spectral ranges.One advantage of this is that continuous variation allows for the targeted investigation of different regions of the signal pulse spectrum, resulting in a more comprehensive characterization of the pulse. This makes it possible to expand the spectral coverage and ensure the adaptability of the method to different signal types.

[0047] According to a further development of the invention, an additional step S 10 is performed in which the phase of the pump pulse is reconstructed taking into account the reconstructed phase of the signal pulse. Reconstruction refers to the computer-aided determination of a physical quantity from measurement data. An advantage of this is that not only the signal pulse but also the pump pulse can be fully described, thus enabling mutual self-calibration of both pulses. This leads to expanded application possibilities, as external references can be dispensed with and both pulses can be accessed independently of each other.

[0048] In step S 10, it is specifically intended that the previously reconstructed signal pulse itself is used as a reference quantity. Assuming certain basic conditions, for example that the signal intensity remains stable in the relevant spectral range or that selected spectral sections of the signal exhibit a constant structure, the phase of the pump pulse can also be determined from the measured interference patterns.

[0049] The method preferably utilizes mutual self-referencing: First, the phase of the signal pulse is derived from the overlap regions with the shaped pump pulse. This information is then used in reverse, with the reconstructed signal pulse being incorporated into the analysis as a known quantity. In this way, the intensity measurements can be unambiguously assigned not only to the signal but also to the pump. The result is a consistent reconstruction of both pulses without the need for an external reference pulse. This approach enables, in particular, a complete description of two initially unknown light pulses, with the mutual use of previously acquired data forming the technical basis for determining the phase of the pump pulse.

[0050] The invention will now be explained in more detail with reference to the drawings and a preferred embodiment.

[0051] The drawings show

[0052] Fig. 1 shows a device according to a preferred embodiment of the

[0053] Invention in a schematic view,

[0054] Fig. 2 shows a schematic representation of the overlap between signal and

[0055] Pump pulse

[0056] Fig. 3 shows a method according to a preferred embodiment of the invention in a schematic diagram.

[0057] Fig. 1 shows a schematic representation of the device 1 according to a preferred embodiment of the invention. A first light source 2 provides a pump pulse 3, which is shaped into two phase-different frequency bins 12 by a pulse shaper 6. A second light source 4 provides a signal pulse 5, which is supplied to the device 1 via a feed line 4. Thus, the device 1 can be coupled to any signal pulse light source, so that the arbitrary signal can be measured with the device 1. The signal pulse 5 is also supplied to the mixing device 7.

[0058] In the mixing device 7, an overlap occurs between the frequency components of the signal pulse 5 and the frequency bins 12 of the pump pulse 3. The intensities of the resulting signals, or rather the part of the signal pulse spectrum that overlaps with the frequency bins 12, are recorded by the measuring unit 9. The evaluation unit 10 reconstructs the phase and / or the coherence properties of the signal pulse from this, and, under certain basic conditions, also the phase of the pump pulse.

[0059] The overlap 11 with the frequency bins 12 is shown in Fig. 2. Fig. 2 schematically shows the spectral overlap 11 between a wide signal pulse 5 and a pump pulse 3 divided into two narrow frequency bins 12 by a pulse shaper. The hatched area represents the overlap 11, i.e., the frequency range in which both pulses 3, 5 are present simultaneously. Only this range contributes to the interference-based measurement in the mixing device 7. By varying the relative phase and / or the frequency spacing 13 between the frequency bins of the pump pulse 3, the phase and coherence of the unknown signal pulse 5 can be reconstructed from the overlap 11.

[0060] Fig. 3 shows a schematic representation of the method according to a preferred embodiment of the invention.

[0061] Figure 3 schematically shows the sequence of process steps S1 to S10. First, in steps S1 and S2, a pump pulse 3 and a signal pulse 5 are provided. In step S3, the pump pulse 3 is shaped so that two phase-different frequency bins 12 are present. In step S4, the pump pulse 3 and signal pulse 5 are mixed, resulting in a first part of the signal pulse spectrum with overlap 11 being output in step S5. The intensity of this part is measured in step S6. Step S7 describes the encoding of a second part with an offset overlap. Step S8 repeats the preceding steps for different relative phases and / or frequency intervals 13. In step S9, the phase and / or coherence properties of the signal pulse 5 are reconstructed.

[0062] Step S10 finally shows the reconstruction of the phase of pump pulse 3, taking into account the previously reconstructed phase of signal pulse 5. Provided that certain conditions are met, such as that the signal intensity remains unchanged in the spectral range of interest or that certain parts of the spectrum retain a fixed structure, conclusions about the phase of pump pulse 3 can also be drawn from the recorded interference signals. Reference symbol list

[0063] 1 Device

[0064] 2 first light source 3 pump pulse

[0065] 4 second light source

[0066] 4' supply line

[0067] 5 signal pulse

[0068] 6 Pulse shaper 7 Mixing device

[0069] 8 first part of the signal pulse spectrum

[0070] 9 Unit of measurement

[0071] 10 evaluation units

[0072] 11 Overlap 12 Frequency Bin

[0073] 13 Frequenzabstand

Claims

Patent claims 1. Device (1) for characterizing the spectral phase of at least one single photon of a signal (5), comprising a first light source (2) for generating at least one pump pulse (3) with a pump pulse spectrum, a feed line (4') for a second light source (4) for feeding at least one signal pulse (5) with a signal pulse spectrum, a pulse shaper (6) for shaping the pump pulse (3) such that two phase-different spectral frequency bins (12) of the pump pulse (3) are forwarded at an adjustable frequency, a mixing device (7) for mixing the shaped pump pulse (3) with the signal pulse (5) and outputting at least a first part (8) of the signal pulse spectrum, wherein the first part (8) comprises an overlap (11) of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse (3),a measuring unit (9) for measuring the intensity of the first part (8) of the signal pulse spectrum and encoding a second part of the signal pulse spectrum, wherein the second part comprises the overlap (11) of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum, an evaluation unit (10) for reconstructing at least one phase and / or one coherence property of the signal pulse (5).

2. Device (1) according to claim 1, wherein the relative phase between the two phase-different frequency bins (12) of the pump pulse (3) is variably adjustable.

3. Device (1) according to claim 1 or 2, wherein the frequency spacing (13) of the frequency bins (12) of the pump pulse (3) is variably adjustable.

4. Device (1) according to one of the preceding claims, wherein the measuring unit (9) is configured to detect the intensities of several outputs of the mixing device (7) in parallel.

5. Device (1) according to one of the preceding claims, wherein the mixing device (7) comprises a quantum pulse gate.

6. Device (1) according to claim 5, wherein the quantum pulse gate is designed to be dispersion-property adapted in order to minimize spectral distortions.

7. Device (1) according to one of the preceding claims, wherein the evaluation unit (10) is designed to reconstruct at least one phase of the pump pulse (3) taking into account the reconstructed signal pulse (5).

8. Method for characterizing the phase of at least one single photon of a signal (5) using the device (1) according to one of the preceding claims, comprising the following method steps: 51 Providing a pump pulse (3), 52 Providing a signal pulse (5), 53 forms of the pump pulse (3) such that two phase-different spectral frequency bins (12) of the pump pulse (3) are provided with an adjustable frequency, 54 Mixing the shaped pump pulse (3) with the signal pulse (5), 55 Outputting at least a first part (8) of the signal pulse spectrum, wherein the first part (8) comprises an overlap (11) of a frequency component of the signal pulse spectrum with the adjustable frequency of the pump pulse (3), 56 Measuring the intensity of the first part (8), 57 Encoding a second part of the signal pulse spectrum, wherein the second part comprises the overlap (11) of the signal pulse spectrum shifted by a predetermined offset and the pump pulse spectrum, 58 Repeat steps S1 to S7 for different relative phases and / or frequency intervals (13) between the spectral frequency bins (12), 59 Reconstructing the phase and / or coherence properties of the signal pulse (5) taking into account the phase of the pump pulse (3).

9. The method of claim 8, wherein in step S8 the relative phase of the frequency bins (12) and / or the frequency spacing (13) of the frequency bins (12) is continuously varied.

10. The method of any one of claims 7 to 9, comprising the following additional method step: S10 Reconstructing the phase of the pump pulse (3) taking into account the reconstructed phase of the signal pulse (5).

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