Measuring arrangement and method for calibratable, direct detection of the quantum state of a single photon or entangled photons

Abstract

The invention relates to a measuring arrangement and a method for calibratable, direct detection of the quantum state of a single photon or entangled photons. The problem addressed by the invention of specifying a measuring arrangement and a method for calibratable, direct detection of the quantum state of a single photon or entangled photons, in which the quantum state of a single photon is detected within a very short time, is solved in that the measuring arrangement comprises a cryostat (1), a tank with liquid nitrogen (2), a tank with liquid helium (3), a cooled movable slide with at least two insertable and exchangeable filters (4), an SNSPD detector (5), at least one turbomolecular pump (6), an aperture (7) for guiding a photon flow, and a gas discharge lamp (8), wherein the bias voltage Ub is applied to the SNSPD detector (5) and an analogue signal is produced in the SNSPD detector (5) when single photons impinge, wherein the measuring arrangement is calibratable and the analogue signal is evaluated in a subsequent evaluation unit in order to extract the quantum number, characterised in that the SNSPD detector (5) is formed by a superconducting material (13) in the form of a single, straight nanowire to which at least two electrical contacts are attached and which is surrounded on its lower face and upper face and on its sides by a layer which is electrically poorly conductive to electrically insulating.

Description

[0001] Measurement setup and method for the calibratable, direct detection of the quantum state of a single photon or entangled photons

[0002] The invention relates to a measuring arrangement and a method for the calibratable, direct detection of the quantum state of a single photon or of entangled photons.

[0003] Electromagnetic radiation consists of photons, with the photon being a physical exchange particle. According to quantum electrodynamics, as the mediator of the electromagnetic interaction, it belongs to the gauge bosons and is therefore an elementary particle. The photon has no mass, but it does possess energy and momentum—both proportional to its frequency—as well as angular momentum. If its environment is confined to a system with finite volume, it contributes to the system's mass proportional to its energy.

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[0005] Photomultipliers, photoconductors, and photodiodes, among other devices, can be used to detect photons. CCDs, vidicons, PSDs, quadrant diodes, and photographic plates and films are used for spatially resolved photon detection. Bolometers are also used in the infrared range. Photons in the gamma-ray range can be detected individually using Geiger counters. Photomultipliers and avalanche photodiodes can also be used for single-photon detection in the optical range, although photomultipliers generally have a lower dark count rate, while avalanche photodiodes can be used even at lower photon energies, extending into the infrared range.

[0006] Photon detection xyiki - Stichen Photodetectors, also known as light sensors or optical detectors, optoelectronic sensors, are electronic components that convert light into an electrical signal using the photoelectric effect or exhibit an electrical resistance dependent on the incident radiation. The term is also used to describe applications that integrate such a radiation-measuring component. In optoelectronics, the term "light" refers not only to visible light but also to invisible infrared and ultraviolet radiation.

[0007] EhotonCTn^hweis wiki -> Search Examples of single-photon detectors are superconducting detectors, such as superconducting nanowire resistors (SNSPDs). 46 ) known.

[0008] Single photon detection wiki - things

[0009] The superconducting nanowire single photon detector (SNSPD or SSPD) is a type of optical and near-infrared single photon detector based on a current-fed superconducting nanowire. It was first developed in 2001 by scientists at Moscow State Pedagogical University and the University of Rochester. The first fully functional prototype was demonstrated in 2005 by the National Institute of Standards and Technology (Boulder) and BBN Technologies as part of the DARPA Quantum Network. As of 2023, a superconducting nanowire single photon detector (SNSPD) is the fastest single photon detector (SPD) for photon counting. It is a key technology for quantum optics and optical quantum technologies. Compared to other types of single photon detectors, SNSPDs offer very high detection efficiency, a very low dark count rate, and very low time jitter.SNSPDs are covered by international standards of the International Electrotechnical Commission (IEC). From 2023, commercial SNSPD devices in multi-channel systems will be available in a price range of €100,000.

[0010] It was recently discovered that superconducting wires with a width of 1.5 pm can detect individual infrared photons. This is important because optical lithography can be used instead of electron lithography in their fabrication. This reduces the cost for applications that require large photodetector areas.

[0011] The SNSPD consists of a thin (~5 nm) or narrow (~100 nm) superconducting nanowire. Its length is typically hundreds of micrometers, and the nanowire is structured in a compact meandering geometry to create a square or round pixel with high detection efficiency. The nanowire is cooled well below its superconducting critical temperature and biased with a DC current close to, but lower than, the nanowire's superconducting critical current. A photon striking the nanowire breaks Cooper pairs and reduces the local critical current to below that of the bias current. This leads to the formation of a localized non-superconducting region, or hotspot, with limited electrical resistance. This resistance is typically greater than the 50-ohm input impedance of the readout amplifier, so most of the bias current is diverted to the amplifier.This generates a measurable voltage pulse approximately equal to the bias current multiplied by 50 ohms. Since most of the bias current flows through the amplifier, the non-superconducting region cools down and returns to the superconducting state. The time it takes for the current to return to the nanowire is typically determined by the nanowire's inductive time constant, which is equal to the nanowire's kinetic inductance divided by the readout circuit's impedance. For proper self-resetting of the device, this inductive time constant must be slower than the intrinsic cooling time of the nanowire hotspot.

[0012] While the SNSPD does not achieve the intrinsic energy or photon number resolution of the superconducting transition edge sensor, it is significantly faster than conventional transition edge sensors and operates at higher temperatures. A certain degree of photon number resolution can be achieved in SNSPD arrays through time-binning or advanced readout schemes. Most SNSPDs are made of sputtered niobium nitride (NbN), which has a relatively high superconducting critical temperature (~10 K), enabling SNSPD operating temperatures in the range of 1 K to 4 K (compatible with liquid helium or modern closed-loop cryocoolers). The intrinsic thermal time constants of NbN are short, allowing for very rapid cooling after photon absorption (<100 picoseconds). [SW^ffife^tiPgja^owire ingle-photon detectOT wiki - Search]

[0013] A single photon is thus an object in spacetime. The single photon is characterized by its direction of propagation z and its quantum numbers. The electric field component of the single photon interacts with polarizable materials. The distribution of the electric field component of single photons depends on the quantum numbers of the single photon. Common quantum numbers are energy, polarization, and orbital angular momentum, and the quantum state of single photons can therefore be determined in terms of these.

[0014] The determination of the quantum state of single photons in the form of orbital angular momentum is known, for example, from the publication [R. Fickler, M. Krenn, A. Zeilinger, Entanglement of photons with orbital angular momentum - Reaching the quantum limit with light screws, Physik unsere Zeit 1 / 2018, DOI: 10.1002 / piuz.201801494], whereby only the recording of many photons (in this case between 674 and 2729) with a sensitive camera shows the characteristic donut structure of the orbital angular momentum.

[0015] It is questionable whether the exact quantum number of orbital angular momentum can even be determined in this way within a reasonable measurement time. For example, the quantum numbers 3> and |-1> are difficult to distinguish with only a small number of photons, around 500 individual photons. Distinguishing the quantum numbers of entangled individual photons becomes even more difficult. Currently, the quantum state of individual photons is determined using an array of single-photon detectors. For example, successive measurements with a large number of individual photons are performed to detect higher excited quantum states, such as the orbital angular momentum of the photons [R. Fickler, M. Krenn, A. Zeilinger, Entanglement of photons with orbital angular momentum – Reaching the quantum limit with light screws, Physik unsere Zeit 1 / 2018, DOI: 10.1002 / piuz.201801494]. This involves conducting experiments with many individual photons to determine the quantum number of the individual photon.However, this requires a long measurement time and subsequent signal analysis of the position measured for each individual photon. US 2005 / 0051726 discloses a single-photon detector comprising a superconducting strip biased near its critical current. The superconducting strip provides a detectable output signal upon absorption of a single incident photon. In one example, the superconductor is a strip of NbN (niobium nitride). In another example, the superconducting strip is coiled to increase the probability of receiving a photon from a light source. The single-photon detector is suitable for a variety of applications, including free-space and satellite communications, quantum communications, quantum cryptography, weak luminescence, and semiconductor device testing.

[0016] The photon detector consists of:

[0017] a superconducting film connected to a bias source,

[0018] wherein the superconducting film is kept at a temperature below its critical temperature and biased near its critical current,

[0019] where the superconducting film is kept in a non-resistive superconducting state and

[0020] wherein the superconducting film has a dimension that enables the detection of a single incident photon by the superconducting strip transitioning from a non-resistive superconducting state to a resistive state.

[0021] The superconducting film consists of niobium nitride, wherein the width of the superconducting film is equal to or less than about 200 nm, so that the superconducting film forms a detectable resistive region upon absorption of the single incident photon.

[0022] This photon detector also includes:

[0023] a multitude of contact surfaces connected to the ends of the superconducting film,

[0024] wherein the bias source is connected to the superconducting film at the multitude of contact surfaces,

[0025] wherein the superconducting film has a meandering structure, the contact surfaces containing gold,

[0026] where at least one photon is coupled to the superconducting film via an optical fiber and

[0027] where the at least one photon is coupled to the superconducting layer via a hemispherical lens.

[0028] The procedure for detecting photons according to US 2005 / 0051726 Al comprises the following steps:

[0029] Providing a superconducting strip maintained at a temperature below its critical temperature and electrically biasing the superconducting strip to a level close to the critical current of the superconducting strip,

[0030] where the superconducting strip is kept in a non-ohmic superconducting state;

[0031] Directing at least one photon at the superconducting strip and thereby capturing the at least one photon striking the superconducting strip by generating an output voltage pulse as a function of the transition of the superconducting strip from a non-ohmic superconducting state to an ohmic state.

[0032] CN 1 16981 342 A discloses a superconducting photon energy resolution detector, a fabrication method, and its application. The superconducting interface photoelectric detection device is fabricated using the superconducting interface material (LAO / KTO), and the photon energy resolution of the detection device is achieved based on this superconducting interface photoelectric detection device, wherein the energy resolution is independent of the wavelength.

[0033] The photon energy resolution superconducting detector is characterized by the fact that a layer of amorphous LAO film is applied to a potassium tantalate substrate using pulsed laser deposition technology, a required pattern is produced using photo-etching, an additional film is produced using ion beam etching, and finally the superconducting interface device is obtained through a peeling process.

[0034] This photon energy-resolving interface superconductivity detector is used for photon energy resolution.

[0035] The process for manufacturing this interface superconductivity detector comprises the following steps:

[0036] (1) Pretreatment of a substrate: Ultrasonic purification of a potassium tantalum substrate in acetone, ethanol and deionized water to obtain a pretreated substrate;

[0037] (2) and (3) Film growth: Growing an amorphous LAO film on a substrate using pulsed laser deposition technology and drying in a vacuum;

[0038] (3) Exposure for photoetching: Application of photoresist to the amorphous LAO film by spin coating, exposure using photolithography and development to obtain a intended structural pattern of the device;

[0039] (4) Ion beam etching: Etching the film obtained in step (3) by ion beam sputtering and transferring the pattern formed by the photoresist onto the LAO film; (5) Removal of the photoresist: and (3) Performing ultrasonic stripping of the film pattern obtained in step (4) in acetone to obtain a clean superconducting LAO / KTO interface device.

[0040] The disadvantage of the previously known technical solution is that measurements with many individual photons require a long measurement time and a subsequent signal analysis of the position measured for each individual photon.

[0041] The object of the present invention is to provide a measuring arrangement and a method for the calibratable, direct detection of the quantum state of a single photon or entangled photons, which avoids the aforementioned disadvantages of the prior art and, in particular, enables the quantum state of a single photon or entangled photons to be detected with only one measurement within a very short time. Furthermore, uses of this measuring arrangement and this method will be described.

[0042] According to the invention, this problem is solved by features of claim 1 and claim 4.

[0043] Further favorable embodiments of the invention are specified in the dependent patent claims.

[0044] The essence of the invention is that, through the provided measuring arrangement and the provided method, which are designed to be calibratable, it is possible to determine the quantum number of a single photon or entangled photons using only a single measurement, instead of several measurements having to be carried out according to the prior art, wherein the time for this measurement is less than 1 nanosecond.

[0045] The measuring setup for the quantum number "energy" includes, for example, a cryostat, a tank with liquid nitrogen (e.g., with T = 77 K), a tank with liquid helium (e.g., with T = 4.2 K), a cooled movable slide with at least two insertable and replaceable filters, an SNSPD detector, at least one turbomolecular pump, an aperture for guiding a photon stream, and a gas discharge lamp, where the bias voltage U b is applied to the SNSPD detector and an analog signal is generated in the SNSPD detector when single photons hit, whereby this analog signal is evaluated in a subsequent evaluation unit to extract the quantum number.

[0046] The SNSPD comprises a single thin, straight superconducting nanowire (e.g., with a thickness in the range of 1 nm - 100 nm, advantageously between 5 and 20 nm for the UV-VIS range, and a width of 1 - 5000 nm, advantageously between 5 - 100 nm for the UV-VIS range) with a length in the nanometer range (e.g., in the range > 200 and < 5500 nm, advantageously < 300 nm) to which at least two electrical contacts are attached, wherein the superconducting nanowire is surrounded on its underside, top side, and sides by a poorly conductive to electrically insulating layer which is simultaneously thermally conductive to very good.

[0047] The electrically poorly conductive to electrically insulating layer consists, for example, of sapphire or Si or SiO2.

[0048] The single, straight superconducting nanowire consists of niobium nitride (NbN), is sputtered with its underside onto the insulating layer and can be temperature controlled via the tank of liquid helium (e.g. with T = 4.2 K), so that a superconducting nanowire single photon detector (SNSPD) is formed within the measuring arrangement.

[0049] Alternatively, the single, straight superconducting nanowire can be made of a different superconducting material, such as Nb, TaN, or Al. The superconducting nanowire is cooled far below its superconducting critical temperature and biased with a direct current that is close to, but lower than, the nanowire's superconducting critical current.

[0050] This involves a single measurement of the peak voltage (y-axis: Peak Voltage) using the SNSPD at a fixed bias current I. b (x-axis: Ib / I c), which determines the quantum number of a single photon (here energy Ei or Ej, with Ei> Ej) or of entangled photons.

[0051] (see Fig. 1A).

[0052] The essential point is that the measurement of the quantum number of a single photon or the quantum number of entangled photons is carried out in the calibratable measurement setup, wherein the measurement setup comprises the superconducting material in the form of the superconducting, single, thin, straight nanowire in the SNSPD detector, to which at least two electrical contacts are attached, wherein the superconducting, thin, straight nanowire is surrounded on its underside and top side as well as on its sides with an electrically poorly conductive to electrically insulating layer, which is simultaneously thermally conductive to very good.

[0053] The superconducting material is characterized by its electrical polarizability and its superconducting properties (critical temperature T, critical current density je, critical magnetic field H, in the case of a type-1 superconductor and Hdl and Ha in the case of a type-II superconductor) and the at least two electrical contacts represent the terminals for a current source.

[0054] The essential aspect of the measurement is that the quantum number of the single photons or the entangled photons is determined via a single measurement using the superconducting material of the SNSPD detector (comprising the superconducting single, thin, straight nanowire) with a single measurement (and not, as in the prior art, with multiple measurements and using nanowires with a compact meander geometry).

[0055] The measuring arrangement is operated in such a way that the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistor R) s ) the minimum current after absorption of a single photon i with quantum number i by the superconducting material differs from the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistance R) s ) of the minimum current after absorption of a single photon j with quantum number j by the superconducting material differs measurably.

[0056] During the measurement, for a given quantum number i of the single photon i, a current IQ^ flows through the superconducting material after absorption of the single photon i, and a voltage drops across the superconducting material.

[0057]

[0058] For a given quantum number j of the single photon j, a current IQ^ flows through the superconducting material after absorption of the single photon j, and a voltage U drops across the superconducting material. Qzj away.

[0059] Thus, the resistance of the measuring setup depends on the quantum number of the absorbed single photon, which is used to calibrate the setup. In addition to the resistance R, other calibration parameters include the temperature T and the magnetic field H.

[0060] The measurement setup includes several filters [e.g. a 200nm Al filter, specifically for transmission through the 200nm Al filter (Al(XUV)) for illumination with single photons from the XUV spectral range and e.g. a 0.5mm Al2O3 filter, specifically for transmission through the 0.5mm Al2O3 filter (Sapphire(VIS)) for illumination with single photons from the VIS spectral range].

[0061] The at least two electrical contacts represent the connections for a power source.

[0062] The measuring arrangement can include at least one shunt resistor R arranged parallel to the superconducting material. sThe setup is designed such that the ambient temperature can be set below TT, the magnetic field can be set to at least above H for a type I superconductor and at least above Ha for a type II superconductor, and the current source provides currents corresponding to a current density greater than j. The shunt resistor is designed to be infinitely large, so that the entire supplied current flows through the superconducting material, or to be between 0 and multiples of the resistance of the superconducting material after absorption of a single photon. The measuring setup is not limited to measuring the quantum number of single photons, but can also be used to measure the quantum number of entangled photons.

[0063] This measuring setup is operated in such a way that the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistor R) s ) the minimum current after absorption of a single photon i with quantum number i by the superconducting material differs from the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistance R) s ) of the minimum current after absorption of a single photon j with quantum number j by the superconducting material differs measurably.

[0064] The invention is explained in more detail below with reference to the schematic drawings and exemplary embodiments. These show:

[0065] Fig. 1: a schematic representation of an embodiment of a measuring arrangement,

[0066] Fig. 1A: a histogram of the measurements with the measuring setup according to Fig. 1 for determining the quantum numbers i and j,

[0067] Fig. 2A: a schematic representation of the quantum number-dependent distribution of the electric field of the single photon i and j for the quantum number energy,

[0068] Fig. 2B: a top view of a section of the straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) and with the quantum number-dependent distribution of the electric field of the single photon i and j according to Fig. 2A for the quantum number energy,

[0069] Fig. 2C: a view of the underside of the electrically poorly conducting to electrically insulating layer (12) according to Fig. 2B, Fig. 3A: a schematic representation of the quantum number-dependent distribution of the electric field of the single photon i and j for the quantum number polarization (of the same energy),

[0070] Fig. 3B: a top view of a section of the straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) and with the quantum number-dependent distribution of the electric field of the single photon i and j according to Fig. 3A for the quantum number polarization (of the same energy),

[0071] Fig. 3C: a view of the underside of the electrically poorly conductive to electrically insulating layer (12) according to Fig. 3B,

[0072] Fig. 4A: a schematic representation of the quantum number orbital angular momentum from the publication [R. Fickler, M. Krenn, A. Zeilinger, Entanglement of photons with orbital angular momentum - Reaching the quantum limit with light screws, Physik unsere Zeit 1 / 2018, DOI: 10.1002 / piuz.201801494] (state of the art),

[0073] Fig. 4B: a top view of a section of the straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) and with the quantum number-dependent distribution of the electric field of the single photon i and j according to Fig. 4A for the quantum number orbital angular momentum,

[0074] Fig. 4C: a view of the underside of the electrically poorly conductive to electrically insulating layer (12) according to Fig. 4B,

[0075] Fig. 5A: a representation of the analog signals during the detection of a photon using an SNSPD with a straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [1Onm NbN on sapphire],

[0076] Fig. 5B: Histograms of the peak voltage of an SNSPD with a straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [1 Onm NbN on sapphire], Fig. 5C: a measurement curve without shunt resistance and calibration curves of an SNSPD with a straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [1 Onm NbN on sapphire],

[0077] Fig. 6: a measurement curve with 50 Ohm shunt resistance and calibration curves of an SNSPD with straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [1Onm NbN on sapphire],

[0078] Fig. 7: a measurement curve without shunt resistance and calibration curves of an SNSPD with straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [20nm NbN on sapphire],

[0079] Fig. 8: a measurement curve with 50 Ohm shunt resistance and calibration curves of an SNSPD with straight superconducting nanowire (11) surrounded by the electrically poorly conducting to electrically insulating layer (12) [20nm NbN on sapphire],

[0080] Fig. 9A: an equivalent circuit diagram of the measuring arrangement without shunt resistor R s ,

[0081] Fig. 9B: an equivalent circuit diagram of the measuring arrangement with a 50 Ohm shunt resistor R s ,

[0082] Fig. 10A: Transmission through 200nm Al filter [Al(XUV)],

[0083] Fig. 10B: Transmission through 0.5nm Al2O3 filter [sapphire(VIS)], Fig. 11: a representation of the photon count rate for SNSPD with 10m NbN thickness on silicon,

[0084] Fig. 12: a representation of the photon counting rate for SNSPD with 20nm NbN thickness on silicon.

[0085] as well as

[0086] Fig. 13: A schematic representation of different types of B bacteriophages. The measuring arrangement shown in Fig. 1 comprises a cryostat (5) equipped with a turbomolecular pump (6), wherein the cryostat (5) has in its interior a tank (2) containing liquid nitrogen (e.g., with T = 77 K) and a tank (3) containing liquid helium (e.g., with T = 4.2 K), a cooled movable slide (4) with at least two insertable and replaceable filters, and an SNSPD detector (5), and into this cryostat (5) a photon stream from a gas discharge lamp (8), guided through an aperture (7), passes through the filters and onto an SNSPD detector (5), wherein two further turbomolecular pumps (6) are located in the region of the aperture (7), and the entire system of the measuring arrangement is hermetically sealed.

[0087] The bias voltage I b is applied via the two connections to the SNSPD detector (5).

[0088] The SNSPD detector (5) is designed such that an analog signal is generated in the SNSPD detector (5) when a single photon hits it, and this analog signal is evaluated in a subsequent evaluation unit to extract the quantum number (not shown in Fig. 1).

[0089] The SNSPD (5) comprises a single thin, straight superconducting nanowire with a diameter in the nanometer range (e.g., with a diameter in the range of > 1 nm and < 50 nm, advantageously between 10 and 20 nm) and with a length in the nanometer range (e.g., in the range of > 10 and < 100 nm, advantageously < 80 nm), to which at least two electrical contacts are attached. The superconducting nanowire is surrounded on its underside, topside, and sides by a poorly conductive to electrically insulating layer. The at least two electrical contacts serve as terminals for a current source (contacts are not shown in Fig. 1). The single photon is characterized by its direction of propagation z and its quantum numbers. The electric field component of the single photon interacts with polarizable materials.The distribution of the electric field component of single photons depends on the quantum numbers of the single photon. Common quantum numbers are the energy E and the polarization.

[0090] Fig. 1A shows a histogram of the measurements with the measuring setup according to Fig. 1 for determining the quantum number E of the photons i and j with Ej~l / kj < E~l / ki.

[0091] For the quantum number energy, the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon, the xy-plane, depends on the wavelength of the single photon (see Fig. 2A).

[0092] In the case of quantum number polarization, the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon (at constant wavelength) depends on the phase angle between the E x -component of the electric field and the E, component of the electric field (see Fig.

[0093] 3A).

[0094] For single photons with the quantum number orbital angular momentum, the distribution of the electric field components E depends x and E y , of the single photon in a plane perpendicular to the propagation direction of the single photon from projection of the orbital angular momentum onto the xy-plane [see Fig. 4A: a representation according to the state of the art (R. Fickler, M. Krenn, A. Zeilinger, Entanglement of photons with orbital angular momentum - With light screws to the quantum limit, Physik unsere Zeit 1 / 2018, DOI: 10.1002 / piuz.201801494] shown, where the recording of many photons (in this case between 674 and 2729) with a sensitive camera shows the characteristic Donat structure of the orbital angular momentum].

[0095] Individual photons have a probability of 0% or 100% of being absorbed at a given location. Therefore, the probability that a single photon is absorbed in the superconducting material of the measurement setup is also either 0% or 100%. If the measurement setup is used for the simultaneous detection of a large number of individual photons (electromagnetic wave of intensity i), o ), then the average number of single photons absorbed in the superconducting material of the measuring setup is to be equated with the intensity drop across the superconducting material.

[0096] The measuring setup calibrated for single-photon measurement can only be used to determine the quantum number of single photons if no other single photons simultaneously strike the measuring setup.

[0097] The measurement setup is calibrated for single photons as follows: Single photons have a probability of 0% or 100% of being absorbed at a given location. Therefore, the probability that a single photon is absorbed in the superconducting material of the measurement setup is also either 0% or 100%. Single photons are prepared in different quantum states, and the resistance of the current path in the superconducting material is measured within the time window in which a normal-conducting cross-section is formed at least at one position of the current path. Calibration is performed for all measurement parameters that change during operation of the measurement setup. These measurement parameters include the global temperature of the measurement setup T and the bias current I. b (Conversion to a bias current density j) b =I b / A Quer(with the cross-sectional area of ​​the current-conducting path in the superconducting material), the shunt resistance, an external magnetic field, constant illumination.

[0098] A single photon absorbed in a superconducting material, whose direction of propagation is defined by z, exhibits a distribution of the electric field component in the xy-plane of the superconducting material that depends on the quantum number of the single photon.

[0099] The extent of the superconducting material in the z-direction is called its thickness D. When a single photon is absorbed in the superconducting material, the electric field component polarizes the charges in the regions where it is non-zero. In the volume of the superconducting material with polarized charges, Cooper pairs are broken up to an increased degree. Each broken Cooper pair yields two normally conducting electrons. Cooper pairs are not scattered when a direct current is driven through a superconducting material. Therefore, no Joule heating is generated during current flow through a superconducting material that is carried exclusively by Cooper pairs.

[0100] However, if Cooper pairs and normal-conducting electrons are present in the volume region of the superconducting material that has been polarized by absorption of a single photon, then Joule heating is generated by scattering of the normal-conducting electrons during current flow through the superconducting material in that volume region. This Joule heating is carried away in all spatial directions from the volume region that has been polarized by absorption of a single photon, in the xy-plane within the superconducting material, and into one or more different slightly electrically conductive to insulating materials on the top surface of the superconducting material, on the side surfaces of the superconducting material, and on the bottom surface of the superconducting material of thickness D.

[0101] The transport of current in the superconducting material and the dissipation of heat from the Joule heat generated during the current flow are a dynamic process in which the volume fraction in the superconducting material containing Cooper pairs as well as normal-conducting electrons initially increases.

[0102] The provided measuring setup (see Fig. 1) is designed such that, within a time window following absorption of the single photon at at least one position of the superconducting material, the current path across the entire cross-section of the conductor is normal conducting. During this time window, the resistance of the measuring setup briefly rises to its maximum value, and the voltage drop across the superconducting and normal conducting cross-sections of the conductor is at its maximum. If the measuring setup includes a shunt resistor, the current flow through the superconducting path and the normal conducting path at the normal conducting cross-section of the conductor is altered within this time window.

[0103] The distribution of the current driven by the measuring system depends in the time window on the ratio of the resistance between the superconducting and normal-conducting path at the position of the normal-conducting cross-section of the conductor and the resistance of the shunt resistor.

[0104] The measurement setup is designed such that, within the given time window, the volume and position of the normal-conducting cross-section depend on the quantum number of the single photon absorbed in the superconducting material. This is achieved by using the surface projection of the quantum-number-dependent distribution of the electric field component of the single photon onto the xy-plane of the superconducting material.

[0105] The method using such a measuring arrangement, in which a photon stream is guided from the gas discharge lamp (8) through the aperture (7) along the at least one turbomolecular pump (6) through one of the at least two insertable and replaceable filters (4) of the cooled movable slide directly onto the SNSPD detector (5), which has a superconducting material (13) in the form of a straight nanowire, wherein the bias voltage Ib is applied to the nanowire of the SNSPD detector (5) and an analog signal is generated in the nanowire of the SNSPD detector (5) when single photons strike it and this analog signal is evaluated in the subsequent evaluation unit to extract the quantum number, comprises, for example, the following three steps:

[0106] • In a first step, the measurement setup is calibrated and a calibration curve for the nanowire is created by recording the histograms of the peak voltage for a selected quantum number under constant experimental conditions for time window, temperature, external magnetic field and ratio of Ib / Ic, and extracting the calibration curve from the analog signals.

[0107] • In a second step, the results of the calibration curves for different Ib / Ic ratios are presented in a common plot, with the peak voltage on the y-axis and the quantum number for which the calibration curves were recorded on the x-axis, and the result of the calibration curves is shown as a function of the quantum number energy, and

[0108] • In a third step, the ratio Ib / Ic is selected for the measurements where the variation of the peak voltage as a function of the quantum number is greatest.

[0109] During the readout step, the focus is placed on determining the peak voltage from the analog signal of the SNPSD upon the impact and absorption of a single photon or entangled photons.

[0110] First embodiment of measurements with a first measuring arrangement

[0111] In a first variant of the design of the measurement setup, the superconducting material is structured for the measurements in such a way that the surface projection of the quantum number-dependent distribution of the electric field component of the single photon onto the xy-plane of the superconducting material (overlap surface) is different.

[0112] This is shown below for three different quantum numbers:

[0113] • for the quantum number of energy at which the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon depends on the wavelength of the single photon (see Fig. 2B),

[0114] • for the quantum number of polarization, where the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon (at constant wavelength) depends on the phase angle between the Ex component of the electric field and the Ey component of the electric field (see Fig. 3B) and • for higher excited quantum numbers, where the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon depends on the higher quantum number (see Fig. 4B).

[0115] For comparison, Fig. 4A shows a representation according to the state of the art [R. Fickler, M. Krenn, A. Zeilinger, Entanglement of photons with orbital angular momentum - Reaching the quantum limit with light screws, Physik unsere Zeit 1 / 2018, DOI: 10.1002 / piuz.201801494], where the recording of many photons (in this case between 674 and 2729) with a sensitive camera shows the characteristic donut structure of the orbital angular momentum.

[0116] The term structuring is not only defined geometrically, but refers to all methods of material processing that modify the superconducting properties of the superconducting material (critical current density, critical magnetic field, critical temperature, pinning center for mobile and pinned vortices, crystal field at the surface for vortice penetration), e.g. ion implantation to create defects or to introduce foreign atoms or to change the chemical composition, or e.g. surface treatment to passivate and change the roughness and thus the crystal field.

[0117] Second embodiment of measurements with a second measuring arrangement

[0118] In a second variant of the measurement setup, at least one of the electrically poorly conductive to electrically insulating materials adjacent to the superconducting material is modified such that the thermal conductivity and the electrical conductivity of the at least one electrically conductive material differ locally. This locally increases or decreases the thermal conductivity. If the thermal conductivity is increased in the volume region of the superconducting material that has been polarized by absorption of a single photon, then this volume region expands less when a current is driven through the superconducting material compared to the other case, in which the thermal conductivity in the volume region of the superconducting material that has been polarized by absorption of a single photon is decreased.

[0119] One advantage is the high thermal conductivity at the surface segments of the superconducting material, where the distribution of the electric field component of the single photon does not differ with different quantum numbers.

[0120] Furthermore, a low thermal conductivity at the surface segments of the superconducting material is advantageous, where the distribution of the electric field component of the single photon differs with different quantum numbers.

[0121] This is shown below for three different quantum numbers:

[0122] • for the quantum number of energy at which the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon depends on the wavelength of the single photon (see Fig. 2C),

[0123] • for the quantum number of polarization, where the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon (at constant wavelength) is determined by the phase angle between the Ex component of the electric field and the E r -component of the electric field depends (see Fig. 3C) and • for higher excited quantum numbers, where the distribution of the electric field component of the single photon in a plane perpendicular to the propagation direction of the single photon depends on the higher quantum number (see Fig. 4C).

[0124] The term "modification of the adjacent material" is not only defined geometrically here, but refers to all methods of material processing that change the electrical conductivity and thermal conductivity of the adjacent material, e.g., through ion implantation to create defects or to introduce foreign atoms or to change the chemical composition, or e.g., surface treatment for passivation and changing the roughness and thus the crystal field.

[0125] Third embodiment: Calibration of the measuring arrangement for single photons

[0126] The measurement setup is calibrated for single photons as follows: Single photons have a probability of 0% or 100% of being absorbed at a given location. Therefore, the probability that a single photon is absorbed in the superconducting material of the measurement setup is also either 0% or 100%. Single photons are prepared in different quantum states, and the resistance of the current path in the superconducting material is measured within the time window in which a normal-conducting cross-section is formed at least at one position of the current path. Calibration is performed for all measurement parameters that change during operation of the measurement setup. These measurement parameters include the global temperature of the measurement setup T and the bias current I. b (Conversion to a bias current density j) b =I b / A Quer with A menthe cross-sectional area of ​​the current-conducting path in the superconducting material), the shunt resistance, an external magnetic field, and constant illumination. The calibration of the measurement setup for distinguishing the quantum number energy of single photons is shown as an example in Fig. 4. In this example, the measurement setup comprises a 10 nm 3 thick NbN layer on sapphire substrate, without shunt resistance, illuminated with single XUV photons, single photons from the visible spectral range and single IR photons and monochromatically at 364 nm.

[0127] In Fig. 5A and Fig. 5B, the measurements taken so far are within the time window at a constant temperature of 4.2 K, without a shunt resistor R. s Voltage curves (see Fig. 5A) and histograms derived from them based on 1000 events each (see Fig. 5B) were recorded without an external magnetic field and without external additional lighting for various bias currents I. bshown. Fig. 5C shows the calibration curve derived from the maxima of the peak voltages (see Fig. 5C).

[0128] Another example is the calibration curves obtained on the same measurement setup using a constant shunt resistance of 50 ohms (see Fig. 6). In this case, less bias current flows through the current path in the superconducting material, and the resistance of the current path in the superconducting material is greater in the time window in which a normal-conducting cross-section is formed at least at one position of the current path (see Fig. 6) compared to the case where the shunt resistance is infinitely large (see Fig. 5C).

[0129] Figure 6 shows the maxima of the peak voltages recorded in the time window at a constant temperature of 4.2 K, a shunt resistance R of 50 ohms, without an external magnetic field and without external additional lighting. The voltage curves are normalized to the critical current 1.

[0130] In Fig. 7 and Fig. 8, the measuring setup comprises a 20 nm thick NbN layer on a sapphire substrate, which is illuminated with single XUV photons, single photons from the visible spectral range and single IR photons.

[0131] Figure 7 shows the maxima of the peak voltages within the time window at a constant temperature of 4.2 K, without a shunt resistance R. s Voltage curves for various bias currents were recorded without an external magnetic field and without external additional lighting. b normalized to the critical current.

[0132] Figure 8 shows the maxima of the peak voltages within the time window at a constant temperature of 4.2 K and a shunt resistor R. s Voltage curves for various bias currents were recorded from 50 ohms, without an external magnetic field and without external additional lighting. / b normalized to the critical current l c shown

[0133] Fourth embodiment: Calibration of the measuring arrangement for entangled single photons

[0134] The measurement setup is calibrated for entangled single photons as follows: Entangled single photons are prepared in different quantum states, and the resistance of the current path in the superconducting material is measured within the time window in which a normal conducting cross-section is formed at least at one position of the current path. Calibration is performed for all measurement parameters that change during operation of the setup, i.e., calibration of the measurement setup for single photons.

[0135] Fifth embodiment: Measuring setup in operation. The equivalent circuit diagram of the measuring setup without shunt resistor R. s is shown in Fig. 9A and the equivalent circuit diagram of the measuring arrangement with shunt resistor R. s is shown in Fig. 9B.

[0136] The measuring setup is shown in Fig. 1. The measuring setup comprises several filters (4). The transmission of a 200 nm Al filter and a 0.5 mm Al2O3 filter is shown as an example in Figs. 10A and 10B.

[0137] Specifically, Fig. 10A shows the transmission through the 200nm Al filter (AI(XUV)) for illumination with single photons from the XUV spectral range and Fig. 10B shows the transmission through the 0.5mm Al2O3 filter (Sapphire(VIS)) for illumination with single photons from the VIS spectral range.

[0138] The filtering of photons according to the quantum number "energy" is examined. This is demonstrated using the analysis of photon count rates (PCR).

[0139] The count rates for an SNSPD with 10 nm 3 NbN thickness on silicon is shown in Fig. 11 across Ib / Ic with a 50 Ohm shunt resistor R. s The results were shown without an external magnetic field and for illumination in different spectral ranges (Al(XUV), Sapphire(VIS), no filter (XUV+VIS)). The filtering is successful, as the modeled sum of weighted measurements with the two filters Al(XUV) and Sapphire(VIS) agrees with the results of the measurement without a filter (no filter (XUV+VIS)).

[0140] The filtering procedure based on the quantum number "energy" is also shown for SNSPDs with a 20 nm NbN thickness on silicon (see Fig. 12). Fig. 12 shows the count rates for an SNSPD with a 20 nm NbN thickness on silicon over I b / h without shunt resistance R s, without an external magnetic field and for illumination in different spectral ranges (AI(XUV), Sapphire(VIS), no filter (XUV+VIS)). The filtering is successful because the modeled sum of weighted measurements with the two filters AI(XUV) and Sapphire(VIS) agrees with the results of the measurement without a filter (no filter (XUV+VIS)).

[0141] A given measuring arrangement is advantageously operated such that the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistor R) sThe minimum current after absorption of a single photon i with quantum number i by the superconducting material differs measurably from the maximum voltage and / or the maximum resistance and / or (when using a finite shunt resistance RS) the minimum current after absorption of a single photon j with quantum number j by the superconducting material. For a given quantum number i of the single photon i, a current I flows after absorption of the single photon i by the superconducting material. Qzi and a voltage U falls across the superconducting material Qzi away.

[0142] For another given quantum number j of the single photon j, a current I flows through the superconducting material after absorption of the single photon j. Qzj and a voltage U falls across the superconducting material Qzj away.

[0143] The use of a current comparator and / or a voltage comparator is advantageous when, for example, it is only necessary to distinguish between single photons i and j with two different quantum numbers i and j. This is of interest in secure digital communication with zero (0) and one (1), in optical computing with digital states of zero (0) and one (1), or in imaging where only two quantum states need to be distinguished.

[0144] The measuring arrangement is designed such that at least one of the two quantities I QZi and I QZj or U QZi and U QZj are distinguishable. The current comparator, for example, uses the average of the two currents I as the reference current. QZi and I QZj (I QZi +I QZj ) / 2. The voltage comparator, for example, takes as its reference voltage the average value between the two voltages Uqa and U. Qz (U QZi +UQZj ) / 2. Do the currents differ? QZi and I QZj If the difference is measurable, then it suffices to compare only the current and measure it with a current comparator to determine the desired quantum number i or j. If the voltages U differ QZi and U QZj If the value is significantly measurable, then it is sufficient to compare only the voltages and measure them with a voltage comparator and determine the desired quantum number i or j.

[0145] The measuring setup consists of a superconducting material to which at least two electrical contacts are attached, and one or more different slightly insulating materials on the top, sides, and bottom of the superconducting material. The superconducting material is characterized by its electrical polarizability and its superconducting properties (critical temperature T, critical current density j). c , critical magnetic field H, in the case of a type-l superconductor and shark and H a in the case of a type II superconductor).

[0146] The at least two electrical contacts represent the connections for a power source.

[0147] The arrangement can include at least one shunt resistor R arranged parallel to the superconducting material. s , included. The arrangement is designed so that the ambient temperature remains below TTThe magnetic field can be adjusted to at least above H for a type-i superconductor and at least above Ha for a type-1l superconductor, and the current source must provide currents corresponding to a current density greater than j. The shunt resistance is designed to be infinitely large, so that the entire supplied current flows through the superconducting material, or to be between 0 and a multiple of the resistance of the superconducting material after absorption of a single photon. The measuring setup is not limited to measuring the quantum number of single photons but can also be used to measure the quantum number of entangled photons. The resistance of the measuring setup depends on the quantum number of the absorbed single photon.The calibration shows the relationship between the resistance of the measuring setup after absorption of a single photon as a function of the quantum state for various bias currents and shunt resistances. Further calibration parameters are the temperature T and the magnetic field H. If the number of determinable quantum numbers is not to be limited, then the resistance of the superconducting material after absorption of the single photon must be measured precisely by determining the current flow through the superconducting material and by determining the voltage drop across the superconducting material in the normal conducting state. If it is sufficient to distinguish between two quantum numbers, then a current comparator and a voltage comparator can be used. This is, for example,of interest in secure digital communication with zero (0) and one (1), in optical computing with digital states with zero (0) and one (1), or in imaging where only two quantum states need to be distinguished, for example two different single-photon energies, two different polarization directions, two different entangled single-photons,...).

[0148] The resistance of the measuring setup can then be determined using a voltage comparator connected in parallel and a current comparator connected in series. The current comparator is required when the shunt resistance R s It is not infinitely large, but finite.

[0149] Sixth embodiment: Use of the measuring arrangement for in vitro imaging of bacteriophages

[0150] The provided measurement setup and method are used for a detector unit of an XUV / EUV microscope in the water window (~285-535 eV, 2.3-4.4 nm) to enable ultrafast, ultrasensitive, and energy-resolved single-photon detection. The high optical contrast between water, carbon, nitrogen, oxygen, and silicon in the water window is used for imaging, with image construction and analysis performed using established classical and quantum image processing techniques.

[0151] Using the XUV / EUV microscope (water window microscope with a superconducting, straight nanowire as an SNSPD detector unit in the water window), in-vitro imaging of voxels smaller (10 nm) is possible. 3 ) 3The provided method makes it possible to generate in-vitro images of lytic bacteriophages (which are currently being intensively researched as an alternative to antibiotics for the treatment of multi-resistant bacteria) without altering their environment or themselves (which is the case with previously known scanning and transmicroscopic examinations due to sample preparation).

[0152] The provided method for calibratable, direct detection of the quantum state of a single photon or the quantum state of entangled photons via in vivo microscopy enables, among other things, rapid counting or taxonomic characterization of bacteriophages (see Fig. 13), as previously known only for prokaryotic and eukaryotic cells using classical light microscopes.

[0153] The proposed technical solution in the form of the device and the method enables the direct determination of the quantum state of a single photon or the quantum state of entangled photons from a single measurement with a single SNSPD in the form of a superconducting, straight nanowire.

[0154] The measurement result is the electrical signal of the SNSPD, which can be read out and further processed.

[0155] This technical solution enables new developments in secure communication with unentangled single photons or with entangled single photons, as well as new developments in optical computing, in the conversion of information stored in the quantum numbers of the single photons into electrical signals.

[0156] This in turn also enables the development of new detectors for image processing, where classically the quantum state of energy is determined using spectral filters and the quantum state of polarization using polarization filters.

[0157] All features described in the description, the exemplary embodiments, and the following claims can be essential to the invention, both individually and in any combination. List of reference numerals

[0158] 1 - Cryostat

[0159] 11 - superconducting material in the form of a single, straight nanowire

[0160] 12 - poorly electrically conductive to insulating material 13 - quantum number-dependent distribution of the electric field of the single photon i and j for the respective quantum number

[0161] 2 - Tank with liquid nitrogen

[0162] 3 - Tank with liquid helium

[0163] 4 - cooled movable slide with filters

[0164] 5 - SNSPD detector with superconducting material (11) 6 - Turbomolecular pump

[0165] 7 - Aperture

[0166] 8 - Gas discharge lamp

[0167] 4A - Overlap region of the quantum number-dependent distribution of the electric field of single photons i and j with increased thermal conductivity in poorly electrically conductive to insulating material. 4B - Non-overlap region of the quantum number-dependent distribution of the electric field of single photons i and j with decreased thermal conductivity in poorly electrically conductive to insulating material.

[0168] i - Photon

[0169] j - Photon

[0170] i - quantum number of the photon i

[0171] j - quantum number of the photon j

[0172] λ - wavelength

[0173] λ1 - shorter wavelength

[0174] λ2 - longer wavelength

Claims

1. Measuring arrangement comprising a cryostat (1), a tank of liquid nitrogen (2), a tank of liquid helium (3), a cooled movable slide with at least two insertable and replaceable filters (4), an SNSPD detector (5), at least one turbomolecular pump (6), an aperture (7) for guiding a photon stream and a gas discharge lamp (8), wherein the bias voltage U ba measurement arrangement is applied to the SNSPD detector (5) and an analog signal is generated in the SNSPD detector (5) when single photons strike it, wherein the measurement arrangement is calibratable and the analog signal is evaluated in a subsequent evaluation unit for the extraction of the quantum number, characterized in that the SNSPD detector (5) is formed by a superconducting material (13) in the form of a single, straight nanowire, on which at least two electrical contacts are attached and which is surrounded on its underside and top side as well as on its sides with an electrically poorly conductive to electrically insulating layer, wherein after calibration by a single measurement with the measurement arrangement the quantum number of a single photon or entangled photons incident on the SNSPD can be determined by measuring the peak voltage that arises after the absorption of the single photon at the SNSPD detector (5),with the nanowire of the SNSPD detector (5) at a fixed bias current (I, b ) is measurable.

2. Measuring arrangement according to claim 1, characterized in that the superconducting material (13) is a nanowire made of NbN and the electrically poorly conductive to electrically insulating layer is simultaneously thermally conductive to very well conductive and consists of Si or SiO2 or sapphire, wherein the thickness is 1–100 nm and is between 5–20 nm for the UV-ViS range, and wherein the width is 1–5000 nm and is between 5–100 nm for the UV-ViS range.

3. Measuring arrangement according to claim 1, characterized in that the filters are, on the one hand, 200 nm Al filters specifically for the transmission of Al(XUV) for illumination with single photons from the XUV spectral range and, on the other hand, 0.5 mm Al2O3 filters specifically for transmission through the sapphire(VIS) for illumination with single photons from the VIS spectral range.

4. Method using a measuring arrangement according to one or more of claims 1 to 3, wherein a photon stream is guided from the gas discharge lamp (8) through the aperture (7) along the at least one turbomolecular pump (6) through one of the at least two insertable and replaceable filters (4) of the cooled movable slide directly onto the SNSPD detector (5), which has the superconducting material (13) in the form of the straight nanowire, wherein the bias voltage I b a single photon is applied to the nanowire of the SNSPD detector (5) and an analog signal is generated in the nanowire of the SNSPD detector (5) when a single photon strikes it and this analog signal is evaluated in the subsequent evaluation unit to extract the quantum number, wherein a single measurement of the peak voltage on the nanowire of the SNSPD detector (5) at a fixed bias current I bthis occurs, which determines the quantum number of a single photon or of entangled photons.

5. Method using a measuring arrangement according to one or more of claims 1 to 3, wherein a photon stream is guided from the gas discharge lamp (8) through the aperture (7) along the at least one turbomolecular pump (6) through one of the at least two insertable and replaceable filters (4) of the cooled movable slide directly onto the SNSPD detector (5), which has the superconducting material (13) in the form of the single, straight, superconducting nanowire, wherein the bias voltage I b is applied to the nanowire of the SNSPD detector (5) and an analog signal is generated in the nanowire of the SNSPD detector (5) when single photons strike it and this analog signal is used in the subsequent evaluation unit for extraction the quantum number is evaluated, the measuring arrangement being operated such that the maximum voltage and / or the maximum resistance and / or, when using a finite shunt resistor, the minimum current after absorption of a single photon i with quantum number i by the superconducting material differs measurably from the maximum voltage and / or the maximum resistance and / or, when using a finite shunt resistor, the minimum current after absorption of a single photon j with quantum number j by the superconducting material, and a current I is measured for a given quantum number i of the single photon i after absorption of the single photon i by the superconducting material. Qzi A voltage U flows across the superconducting material. Qzi falls off and for another given quantum number j of the single photon j, after absorption of the single photon j by the superconducting material, a current I Qzj flows and a voltage U is generated across the superconducting material Qz j ab falls.

6. Method using a measuring arrangement according to one or more of claims 1 to 3, wherein a photon stream is guided from the gas discharge lamp (8) through the aperture (7) along the at least one turbomolecular pump (6) through one of the at least two insertable and replaceable filters (4) of the cooled movable slide directly onto the SNSPD detector (5), which has the superconducting material (13) in the form of a straight nanowire, wherein the bias voltage I b is applied to the nanowire of the SNSPD detector (5) and an analog signal is generated in the nanowire of the SNSPD detector (5) when single photons strike it and this analog signal is evaluated in the subsequent evaluation unit to extract the quantum number, wherein • In a first step, the measurement setup is calibrated and a calibration curve for the nanowire is created, in which the histograms of the peak voltage for a selected quantum number under constant experimental conditions for time window, temperature, external magnetic field and ratio of Ib / Ic are plotted. are recorded and the calibration curve is extracted from the analog signals, • In a second step, the results of the calibration curves for different Ib / Ic ratios are presented in a common plot, with the peak voltage on the y-axis and the quantum number for which the calibration curves were recorded on the x-axis, and the result of the calibration curves is shown as a function of the quantum number energy, and • In a third step, the ratio Ib / Ic is selected for the measurements where the variation of the peak voltage as a function of the quantum number is greatest.

7. Method according to claim 4, 5 or 6, characterized in that in the calibration step the dependence of the resistance of the nanowire of the SNSPD detector (5) on the quantum number of the absorbed single photon is used to calibrate the measuring arrangement and to create the calibration curve.

8. Method according to one or more of claims 1 to 7, characterized in that, during the single measurement step, the maximum voltage and / or the maximum resistance and / or, when using a finite shunt resistor RS, the minimum current after absorption of a single photon i with quantum number i by the superconducting material of the SNSPD detector (5) differs measurably from the maximum voltage and / or the maximum resistance and / or, when using a finite shunt resistor RS, the minimum current after absorption of a single photon j with quantum number j by the superconducting material of the SNSPD detector (5), wherein • for a given quantum number i of the single photon i after absorption of the single photon i by the superconducting material of the SNSPD detector (5) a current I Qzi flows and a voltage U is applied across the superconducting material of the SNSPD detector (5) Qzi falls and • for another given quantum number j of the single photon j after absorption of the single photon j by the superconducting material of the SNSPD detector (5) a current I Qz j flows and a voltage U is applied across the superconducting material of the SNSPD detector (5). Qzj falls off.

9. Method according to one or more of claims 1 to 8, characterized in that the focus of the readout step is on determining the peak voltage from the analog signal of the SNSPD upon the impact and absorption of a single photon or entangled photons.

10. Use of the measuring arrangement according to claims 1 to 3 and of the method according to claims 4 to 9 for typing bacteriophages using an XUV / EUV microscope in the form of a water window microscope with a superconducting, straight nanowire as an SNSPD detector unit in the water window, wherein in vitro imaging of voxels smaller than 10 nm 3 This has been done.

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