A method for operating a photonic circuit

Abstract

The invention relates to a method for operating a photonic circuit (50), in particular a four-rail photonic gate, for the generation of entangled light states (1-8), which method comprises steps for the periodic generation of several spatially compressed and separated light states (1-8), for the spatially separated feeding of the compressed light states (1-8) into the photonic circuit (50), for the pairwise transformation of the compressed light states (1-8) into EPR pairs, and for applying at least one time-division multiplexing operation to at least two EPR pairs, in particular to two light states (1-8) from different EPR pairs, for the generation of an entangled cluster state. Figure for the abstract: Fig. 2

Description

Title of the invention: Method for operating a photonic circuit. Technical field

[0001] The application relates to a method for operating a photonic circuit to generate entangled light states. Other objects of the invention form a photonic circuit as well as a quantum computer. Background

[0002] Photonic circuits used for entangling generated light states are known as such. Light states entangled in such photonic circuits are used in particular in quantum computers. These circuits are generated using free-space structures (free-space optics, FSO). These consist of either purely time-division multiplexing or purely space-division multiplexing. This technique is very space-intensive and therefore cannot be used in photonic integrated circuits.

[0003] In this technique, maintaining the phase stability of the structure is also very difficult because free-space structures are highly vulnerable to mechanical and other sources of interference. However, sufficient phase stability is a fundamental requirement for quantum computing applications.

[0004] Furthermore, known free-space structures generate only a limited amount of entanglement, which is not directly scalable to larger systems. Therefore, scalability beyond a few qubits is not possible with current techniques, and thus current photonic circuits are not suitable for photonic quantum computers. Summary

[0005] The objective of the present invention is therefore to indicate a possibility of entanglement of light states suitable for photonic quantum computers.

[0006] This objective is resolved in a method for operating a photonic circuit, in particular a four-rail photonic gate of the type initially mentioned, by the fact that the method comprises steps for the periodic generation of several spatially separated compressed light states, for the spatially separated supply of the compressed light states to the photonic integrated circuit, for the pairwise transformation of the compressed light states into EPR pairs (Einstein-Podolsky-Rosen pairs), and for applying at least one time-division multiplexing operation to at least two EPR pairs, in particular to two light states of different EPR pairs, for the generation of an entangled cluster state.

[0007] During the periodic generation of several spatially compressed and separated states of light, several spatially compressed and separated states of light are generated at a given instant. Identical compressed states of light are regenerated after a predefined period, so that spatially separated time sequences of identical compressed states of light are generated. The compressed and spatially separated states of light are therefore identical, whereas the spatially compressed and separated states of light may not be identical. The non-identical states of light may, for example, differ in terms of the (average) number of photons and / or their phase-space orientation and / or exhibit different levels of compression.

[0008] Compressed light states exhibit a certain degree of compression in their phase-space quadrature. In this way, light states can lead to a cluster state suitable for CV quantum computing (continuous-variable quantum computing) because CV quantum computing requires a compressed, multimodal Gaussian state as a resource state.

[0009] Before being fed into the photonic circuit, the compressed light states can be filtered so that compressed light states as free from noise as possible are fed into the photonic circuit, in particular for use in a quantum computer.

[0010] The separate supply of compressed light states in space can, for example, be achieved in waveguides of the circuit, which are different and separated from one another. The waveguides can be part of a photonic chip. In this way, the size can be reduced, in particular by a factor of more than 100 compared to conventional free-space structures. The photonic circuit can thus be implemented as a photonic integrated circuit and, in particular, be fully integrated into a photonic chip.

[0011] In the circuit, the compressed light states can be transformed in pairs into EPR pairs, that is, into Einstein-Podolsky-Rosen pairs, also known as Bell states. The conversion of two compressed light states into an EPR pair can be easily accomplished by means of a beam splitter with which the two compressed light states are entangled. The phase-space orientation of the two compressed light states can be variably designed, in particular by means of a phase shifter. In particular, a compressed light state p can be transformed into an EPR pair with a compressed light state q by means of from an interaction of beam splitters, particularly after one of the light states has passed through a 90-degree phase shifter.

[0012] The time-division multiplexing operation allows for the entanglement of at least two EPR pairs, the EPR pairs, or at least one light state of the EPR pairs, being separated from each other in time. Preferably, this time-division multiplexing operation can be performed by entangling two light states of two EPR pairs that are not separated from each other in time, at least one of the remaining light states of the two EPR pairs, in particular the two remaining light states of the two EPR pairs, being separated in time with respect to the two light states that are not separated from each other in time and / or being separated from each other in time.

[0013] By combining spatial and temporal multiplexing, a large entangled cluster state can be generated using different compressed light states. Furthermore, improved phase stability and long-term stability compared to free-space structures can be achieved. An entanglement of light states is thus obtained, which is suitable for photonic quantum computers.

[0014] In this context, it has proven advantageous for at least one light state of at least one EPR pair to be time-shifted relative to the other light state of the EPR pair. The time shift of at least one light state of at least one EPR pair makes it easy to perform a time-division multiplexing operation. Preferably, the light states of several, in particular two, non-identical EPR pairs are time-shifted. Two EPR pairs are non-identical if the light states of one EPR pair are not identical to the light states of the other EPR pair. To generate the time-shifted EPR states, the photonic circuit can incorporate delay lines.

[0015] In the context of the improvement of the invention, at least one time-shifted light state of at least one EPR pair is entangled with the complementary light state of an identical EPR pair that is later in time. This entanglement makes it easy to perform a time-division multiplexing operation with two EPR pairs. A complementary light state refers to the second light state that forms an EPR pair together with a first light state (for example, the time-shifted light state) or a light state identical to the first light state, that is, a light state generated in the time sequence preceding or following the first light state, but otherwise identical. Two EPR pairs are identical if the light states of one EPR pair are identical to the light states of the other EPR pair.

[0016] According to one design, it is proposed that four states of light are entangled by means of beam splitter interactions such that at least one A spatial four-rail gate node is created. In a spatial four-rail gate node, four non-entangled and spatially separated light states can be transformed into four interentangled and still spatially separated light states. The entanglement of the four light states through beam splitter interactions can be designed such that each light state is entangled with at least two other light states. Preferably, each of the four light states belongs to a different EPR pair. Particularly preferred, the light states of at least three non-identical EPR pairs are entangled with each other to generate at least one spatial four-rail gate node. A photonic circuit with a four-rail gate node can represent a four-rail gate in which four light states are entangled with each other.

[0017] Preferably, the photonic circuit comprises two spatial four-rail gate nodes. Preferably, eight light states are fed into the photonic circuit and transformed into four non-identical EPR pairs. A photonic circuit comprising two four-rail gate nodes can represent a four-rail gate in which eight light states are transformed into two groups of light states entangled with each other.

[0018] As part of the improvement of the invention, it is proposed that at least one spatial four-rail gate node be formed from a time-non-shifted light state of a first EPR pair, a complementary time-shifted light state of an identical time-previous EPR pair, a time-non-shifted light state of a second EPR pair, and a time-non-shifted light state of a third EPR pair. In this way, only one time-shifted light state is required to generate the four-rail gate node. Advantageously, the two light states of the second and / or third EPR pair are time-non-shifted.

[0019] In this context, it has proven advantageous to intertwine the time-shifted light state of the EPR pair identical to the first EPR pair and / or the non-time-shifted light state of the third EPR pair of at least one spatial four-rail gate node with the non-time-shifted light state of the first EPR pair and the non-time-shifted light state of the second EPR pair, respectively. In particular, EPR pairs identical to each other and exhibiting a time-shifted light state can be connected in this way to the remaining EPR pairs of the four-rail gate node, especially those that do not exhibit a time-shifted light state.

[0020] According to a preferred design, at least one spatial four-rail gate node is multiplexed several times in time. Time multiplexing can be performed By intertwining several light states of the spatial four-rail gate node, specifically at least one light state from a pair of EPRs, with a time-shifted light state of the same spatial four-rail gate node, two time-separated four-rail gate nodes can be connected to each other via the time-shifted and non-time-shifted light states of the same EPR pair. This connection can be made such that the non-time-shifted light state of the EPR pair is part of a first spatial four-rail gate node, while the complementary time-shifted light state of the same EPR pair is part of a second, time-later four-rail gate node.Multiple time-division multiplexing can be performed by intertwining a light state of the spatial four-rail gate node with a time-unshifted light state complementary to the time-shifted light state of the same EPR pair. This complementary time-unshifted light state can connect the spatial four-rail gate node to a spaced four-rail gate node in the opposite time direction. In this way, a connected time chain of space four-rail gate nodes can be generated, which can continue in both time directions.

[0021] It is possible that at least one light state may be out of phase between two beam splitter interactions. A phase shift between two beam splitter interactions allows for targeted correction or modification of the phase of the light state. The phase shift can be induced by a phase shifter in the photonic circuit. The phase shifter can be arranged between two beam splitters in the photonic circuit.

[0022] In another embodiment of the invention, the quadrature values ​​encoded in the compressed light states are measured using homodyne detection at the end of the photonic circuit. By means of homodyne detection, the state values ​​at the end of the photonic circuit can be easily read to capture the result of quantum computing.

[0023] In this context, it has proven advantageous to generate interference from the respective light state at the end of the photonic circuit and a reference radiation, in particular by means of a tunable directional coupler, preferably set to a 50 / 50 splitting ratio, and to use it in conjunction with the reference radiation during homodyne detection. In this way, it is possible to generate signals suitable for detection and evaluation. The interference generated from the different light states, in particular by means of the directional coupler, is transmitted to detectors in parallel with the reference radiation via detector outputs of the photonic circuit. The detectors, in particular symmetrical ones, can detect intensity differences between two detector outputs associated with a state of light, in particular the interference and reference radiation associated with the state of light.

[0024] The reference radiation can be easily generated by means of an external local oscillator connected to the lasers generating the compression. In this way, the reference radiation can be matched to the respective laser radiation used to generate the compression of the initial light state. The phase of the local oscillator can be modified for tuning purposes with fast phase shifters, which are respectively associated with one of the lasers generating the compressions. These fast phase shifters can be induced by electro-optical modulation in an InP chip to generate and emit the reference radiation.

[0025] Preferably, a difference in intensity measured over a predefined time interval is integrated. In this way, statistical quantum properties can be captured. The output quadrature can, in particular, be measured by convolution with a response function.

[0026] According to one embodiment of the invention, it is proposed that at least one detector output be connected to a photon-number-resolving detector, in particular a PNR-SNSPD or a TES. A PNR-SNSPD (photon-number-resolving superconducting nanowire single-photon detector) or a TES (transition edge sensor) can provide reliable and accurate photon-number-resolving measurements. By implementing photon-number-resolving measurements at this detector output, it is possible to implement non-Gaussian gates, particularly cubic ones.

[0027] In the case of a photonic circuit, in particular a photonic integrated circuit of the type initially mentioned, it is proposed, in order to solve the previous problem, that it be configured to implement the method described above, which makes it possible to obtain the advantages described in relation to the method.

[0028] The characteristics described in relation to the method according to the invention can also be applied to the photonic circuit, individually or in combination. This results in the same advantages as those described above.

[0029] According to one constructive design, it is proposed that the photonic circuit has at least one interconnection of four quadruple beam splitters to generate a four-rail spatial gate node. This interconnection can have four inputs, each for a different light state. The interconnection can, in particular, be implemented in several stages.

[0030] A first stage of the interconnection may have two quadruple beam splitters whose inputs form the four inputs of the interconnection.

[0031] A second interconnection stage may have two additional quad beam splitters, the first input of which is connected to an output of a first quad beam splitter of the first stage, and the second input of which is connected to an output of a second quad beam splitter of the first stage. The inputs of the quad beam splitters of the second stage can thus be connected to different outputs of different quad beam splitters of the first stage.

[0032] Phase shifters can be mounted downstream of the outputs of the quad beam splitters of the first stage and / or the outputs of the quad beam splitters of the second stage. The outputs of the quad beam splitters of the first stage and the inputs of the quad beam splitters of the second stage can be connected via the phase shifters mounted downstream of the quad beam splitters of the first stage.

[0033] Preferably, the photonic circuit may have two parallel interconnections of four quadruple beam splitters to generate two four-rail space gate nodes. This can easily generate a four-rail space gate node.

[0034] In the case of a quantum computer of the type initially mentioned, it is proposed, in order to solve the previous problem, that it be configured to implement the process described above and / or that it have a photonic circuit designed in the manner described above, which makes it possible to obtain the advantages described in relation to the process and the photonic circuit.

[0035] The characteristics described in relation to the method according to the invention and the photonic circuit can also be applied to the quantum computer, individually or in combination. This results in the same advantages as those described above. Brief description of the drawings

[0036] Embodiments, improvements, and examples of the invention are explained in more detail below with reference to the accompanying drawings. The figures show:

[0037] [Fig-1] a schematic structure of the generated cluster state and

[0038] [Fig.2] a schematic structure of the photonic circuit for the implementation of the process. Detailed description

[0039] Figure 1 shows the schematic structure of the cluster state generated by the method according to the invention, which cluster state is obtained at the end of the photonic circuit 50. This consists of several compressed and separated light states 1-8 in space, that is to say they are separated from each other in space and also propagate separately from each other in space through the photonic circuit 50. It is only in the quadruple beam splitters 11 described below that the said space-separated states of light 1-8 interact with each other.

[0040] The light states 1-8 are generated at periodic intervals such that a temporal sequence of identical light states 1-8 results. For example, light state 1 is generated at a given first instant. After a predefined period, an identical light state 1 is generated again.

[0041] This time sequence of spatially separated light states 1-8 is fed into the waveguides 9 of the photonic circuit 50, shown in [Fig. 2]. For each of the spatially separated light states 1-8, the circuit 50 has its own waveguide 9, so that the light states 1-8 continue to be spatially separated, even when they pass through the photonic circuit 50.

[0042] In the photonic circuit 50, respectively a pair of said light states 1-8 is transformed into an EPR pair. In [Fig. 1], this is symbolized by the thick connecting line between the light states 1, 2; 3, 4; 5, 6; 7, 8.

[0043] For the generation of said EPR pairs, the light states 1-8 are conducted in a first zone A of the circuit 50 respectively to an input of a quadruple beam splitter 11, such that each pair of the light states 1-8 is entangled with the other. The two light states 1-8 of said EPR pairs then exit the quadruple beam splitters 11 at their outputs. The respective phase of the light states 1-8 can be further adjusted by means of a phase shifter 12 mounted downstream.

[0044] In the first zone A of the photonic circuit 50, the waveguides of the two light states 2 and 6 further each have a delay line 10. By means of said delay line 10, the light states 2 and 6 are time-shifted. Whereas the complementary light states 1 and 5 of the EPR pairs coformed by the light states 2 and 6 are not time-shifted.

[0045] In [Fig. 1], this time shift of light states 2 and 6 is recognizable in that they are represented along the time axis T at time t2, while the remaining light states 1, 3, 4, 5, 7, 8 supplied with them in the circuit 50 are represented at time t1. Consequently, the thick line symbolizing the EPR pair between light states 1 and 2 as well as between light states 5 and 6 in [Fig. 1] extends horizontally, while it extends vertically for the EPR pairs consisting of two light states 3, 4, 7, 8 not shifted in time.

[0046] The time shifts caused by the delay lines 10 are tuned to the generation period of the spaced-out light states 1-8 such that that light states 2 and 6 are shifted by one period. At the end of the first zone A of circuit 50, the time-shifted light states 2 and 6 therefore arrive simultaneously with the light states 1, 3, 4, 5, 7, and 8, which are powered later at time t2, although they remain separated in space. The light states 1, 3, 4, 5, 7, and 8, powered simultaneously with the time-shifted light states 2 and 6, have already reached the end of the first zone A at time t1. On the other hand, light states 2, 6 supplied at the same time as light states 1, 3, 4, 5, 7, 8 supplied later, which reach the end of the first zone A at time t2, are also shifted in time, so that said light states only reach the end of the first zone A at time t3.

[0047] Light states 1, 3, 4, 5, 7, and 8 then enter the second zone B of the photonic circuit 50 simultaneously with time-shifted light states 2 and 6. This zone has two interconnections 15 of quadruple beam splitters 11, which are used to generate four-rail gate nodes 17. In the four-rail gate nodes 17, light states 1-8 are entangled with each other via EPR pairs through beam splitter interactions. The two interconnections 15 are connected to each other in parallel.

[0048] The two interconnections 15 respectively have two stages of two quadruple beam splitters 11 connected in parallel.

[0049] In the first interconnection 15 shown on the left in [Fig. 2], the light state 1 is first entangled, at the first stage, with the time-shifted light state 2. This entanglement through an interaction of beam splitters is possible because the light state 1 and the time-shifted light state 2 are not separated from each other in time. The light state 1 (at time t1), which forms an EPR pair with the time-shifted light state 2, and the time-shifted light state 2 at time t3, which forms an EPR pair with the light state 1 that is entangled with the time-shifted light state 2 at time t2, are separated from the two entangled light states 1, 2 at time t2 by an interaction of beam splitters and are spaced from each other in time.There is therefore a time-division multiplexing in which light state 1 is connected, via the time-shifted light state 2, to the preceding light state 1, which forms an EPR pair with the time-shifted light state 2. The entanglement of light state 1 with the time-shifted light state 2 is symbolized in [Fig. 1] by a thinner connecting line between light states 1 and 2 at time t2. The connection from light state 1 at time t2 to light state 1 at time t1 can be traced using the connection via the solid lines. The same applies to the time-shifted light state 2 at time t3.

[0050] Simultaneously, at the first stage of the first interconnection 15, the light state 3 is entangled with the light state 8 by an interaction of beam splitters. To achieve this, two time-non-shifted light states 3, 8 of non-identical EPR pairs are entangled with each other.

[0051] In the second stage of the first interconnection 15, the light state 1 from the left output of the left quadruple beam splitter 11 of the first stage is entangled with the light state 8 from the right output of the right quadruple beam splitter 11 of the first stage. Similarly, the time-shifted light state 2 from the right output of the left quadruple beam splitter 11 of the first stage is entangled with the light state 3 from the left output of the right quadruple beam splitter 11 of the first stage.

[0052] At the end of the second zone B of the circuit 50, the entanglement of the light states 1, 2, 3, and 8 shown in [Fig. 1] is thus established. In this, two light states 3, 8 from two non-identical EPR pairs, which are formed by light states 3, 4, 7, 8 not shifted in time, are connected to two light states 1, 2 from EPR pairs identical to each other, one of these light states 2 being shifted in time. In this way, a four-rail gate node is formed, which connects four EPR states to each other, one of which extends over the time domain.

[0053] Similarly, at a first stage of the second interconnection 15 shown on the right in [Fig.2], the time-unshifted light state 4 is first entangled with the time-unshifted light state 5 by a quadruple beam splitter 11. Simultaneously, the time-shifted light state 6 is entangled with the time-unshifted light state 7.

[0054] In the second stage of the second interconnection 15, the light state 4 from the left output of the left quadruple beam splitter 11 of the first stage is entangled with the light state 7 from the right output of the right quadruple beam splitter 11 of the first stage. Similarly, the light state 5 from the right output of the left quadruple beam splitter 11 of the first stage is entangled with the time-shifted light state 6 from the left output of the right quadruple beam splitter 11 of the first stage.

[0055] In the represented design of the photonic circuit 50, a phase shifter 12 is arranged in the waveguide 9 after each output of a quadruple beam splitter 11.

[0056] At the end of the second zone B of the photonic circuit 50, the entanglement of the light states 4-7 shown in [Fig. 1] is also established. In this, two light states 4, 7 of two non-identical EPR pairs, which are formed by light states 3, 4, 7, 8 not shifted in time, are connected to two light states 5, 6 of EPR pairs identical to each other, one of these light states 6 being shifted in time. In this way, the four-rail gate node 17 is formed, which connects four EPR states to each other, one of which extends over the time domain. This four-rail gate node 17 is highlighted by a circle surrounding it in [Fig. 1].

[0057] While EPR pairs with time-shifted 2,6 light states connect several four-rail gate nodes 17 to each other in the time domain, EPR pairs without time-shifted 2,6 light states thus connect several four-rail gate nodes 17 to each other in the space domain.

[0058] Using the cluster state shown in [Fig. 1] after passing through zones A and B of the photonic circuit 50, it can be seen that this circuit 50 makes it possible to obtain a large entangled cluster state from a plurality of EPR states. These entanglements are not limited to spatial entanglements, but also connect time-spaced light states to time-shifted light states via EPR pairs. This combination of spatial and temporal multiplexing makes it possible to generate large entangled cluster states with a large number of entanglements that are directly scalable to larger systems. The photonic circuit 50 can be easily adapted to a larger system by increasing the number of interconnections 15 or by using interconnections 15 with additional stages.

[0059] In a final zone C, the photonic circuit 50 has several directional couplers 13. The waveguides 9 associated with the light states 1-8 each terminate in such a directional coupler 13. In addition to the respective light state 1-8, reference radiation is directed to the respective directional coupler 13. The reference radiation is generated by means of a local oscillator 16, downstream of which are mounted eight fast phase shifters (not shown) to modify the phase of the local oscillator 16. These fast phase shifters are connected to the lasers (not shown) that generate the compressed light states 1-8. These fast phase shifters are induced by electro-optical modulation in an InP chip that emits the respective reference radiation. This chip is directed via a fiber to the respective directional coupler 13.

[0060] The interference of the compressed light and the local oscillator, generated by means of the respective directional coupler 13, is distributed via the outputs of detectors 14 to which can be connected, for example, homodyne detectors, TES or PNR-SNSPD to measure the light states 1-8 of the cluster state. List of reference signs

[0061] 1-8 States of light

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] 9 Waveguides 10 Delay Line 11 Quadruple Beam Splitter 12 Phase Shifter 13 Directional Coupler 14 Detector Output 15 Interconnect 16 Oscillator 17 Four-Rail Gate Node 50 Photonic Circuit tl-t3 Instants A Zone B Zone C Zone T Time Axis

Claims

Demands

1. 1 A method for operating a photonic circuit (50), in particular a four-rail photonic gate, for the generation of entangled light states (1-8), comprising the steps of: # periodically generating several spatially compressed and separated light states (1-8); # spatially feeding the compressed light states (1-8) into the photonic circuit (50); # pairwise transforming the compressed light states (1-8) into EPR pairs; # applying at least one time-division multiplexing operation to at least two EPR pairs, in particular to two light states (1-8) from different EPR pairs, for the generation of an entangled cluster state.

2. 2 Method according to claim 1, characterized in that at least one light state (2, 6) of at least one EPR pair is time-shifted relative to the other light state (1, 5) of the EPR pair.

3. 3 Method according to claim 2, characterized in that at least one time-shifted light state (2, 6) of at least one EPR pair is entangled with the complementary light state (1, 5) of an identical time-later EPR pair.

4. 4 Method according to any one of the preceding claims, characterized in that four states of light (1, 2, 3, 8; 4, 5, 6, 7) are entangled with each other by means of beam splitter interactions such that at least one spatial four-rail gate node (17) is created.

5. 5 Method according to claim 4, characterized in that at least one spatial four-rail gate node (17) is formed from a time-non-shifted light state (1,5) of a first EPR pair, a time-shifted complementary light state (2,6) of an identical time-earlier EPR pair, a time-non-shifted light state (3,7) of a second EPR pair and a time-non-shifted light state (8,4) of a third EPR pair.

6. 6 Method according to claim 5, characterized in that the time-shifted light state (2, 6) of the EPR pair is identical to the first pair EPR and / or the (4, 8) time-nonshifted light state of the third pair EPR of Pau at least one spatial four-rail gate node are respectively entangled in the (1,5) time-nonshifted light state of the first pair EPR and in the (3, 7) time-nonshifted light state of the second pair EPR.

7. 7 Method according to any one of the preceding claims 4 to 6, characterized in that at least one spatial four-rail gate node (17) is multiplexed several times in time.

8. 8 Method according to any one of the preceding claims 4 to 7, characterized in that at least one state of light (1-8) is out of phase between two interactions of beam splitters.

9. 9 Method according to any one of the preceding claims, characterized in that quadrature values ​​coded in the compressed light states (1-8) are measured using homodyne detection at the end of the photonic circuit (50).

10. 10 Method according to claim 9, characterized in that an interference of the light states (1-8) at the end of the photonic circuit (50) and a reference radiation, in particular by means of a tunable directional coupler (13), preferably set to a distribution ratio of 50 / 50, is generated and used jointly with the reference radiation during homodyne detection.

11. 11 Method according to any one of the preceding claims 9 or 10, characterized in that a measured intensity difference is integrated over a predefined time interval.

12. 12 Method according to any one of the preceding claims, characterized in that at least one detector output (14) is driven to a photon number resolution detector, in particular a PNR-SNSPD or a TES.

13. 13 Photonic circuit (50), in particular photonic integrated circuit, configured for implementing the method according to any one of claims 1 to 12.

14. 14 Photonic circuit (50) according to claim 13, characterized by at least one interconnection (15) of four quad beam splitters (11) for the generation of a spatial four-rail gate node (17).

15. 15 Quantum computer, characterized in that it is configured for the implementation of the method according to any one of the claims 1 to 12 and / or includes a photonic circuit (50) according to any one of claims 13 or 14.

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