A travelling wave parametric amplifier system

Abstract

The present disclosure relates to an amplifier system (200) comprising at least four travelling wave parametric amplifiers (210a-d), TWPA, parallel connected between a first and second interferometer system (220, 240). The amplifier system (200) further comprises a set of pump couplings (230a-l). Each pump coupling being configured to couple a pump tone to at least one of at least one input port (202a-b) of the first interferometer system (220) and / or a respective input port (212a-d) of the TWPAs (210a-d) and / or a respective output port (214a-d) of the TWPAs (21 Oa-d) and / or at least one output port (208a-b) of the second interferometer system (240).

Description

[0001] AMPLIFIER SYSTEM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to amplifier systems, in particular travelling wave parametric amplifier systems.

[0004] BACKGROUND ART

[0005] The basic amplification principle of a travelling wave parametric amplifier, TWPA, is based on the interaction between a weak signal and a strong co-propagating wave, called the pump, when propagating through a nonlinear medium. Under a certain phasematching condition this can result in an exponential spatial growth of the signal amplitude while also generating another wave called the idler.

[0006] Properties of an ideal amplifier system includes providing a large band with high gain and quantum-limited noise performance. The amplifier system should also have minimal back-action on the sample(s) and ideally only output the desired signal. To prevent back- propagation of noise and other tones from what comes after the amplifier system, isolation is often also a desired property of the amplifier.

[0007] There is a need in the art for amplifier systems providing and / or improving upon said properties.

[0008] SUMMARY OF THE INVENTION

[0009] The present disclosure relates to an amplifier system. The amplifier system comprises a first interferometer system. The amplifier further comprises at least two travelling wave parametric amplifiers, TWPA. The amplifier system also comprises a second interferometer system. The first interferometer system comprises at least one input port, and at least one output port per TWPA. The second interferometer system comprises at least one output port, and at least one input port per TWPA. Each TWPA comprises an input port and an output port. The input port of each TWPA is connected to a respective output port of the first interferometer system. The output port of each TWPA is connected to a respective input port of the second interferometer system. According to some aspects, the amplifier system further comprises a set of pump couplings. Each pump coupling is configured to couple a pump tone to at least one of the at least one input port of the first interferometer system and / or a respective input port of the TWPAs and / or a respective output port of the TWPAs and / or at least one output port of the second interferometer system.

[0010] The disclosed amplifier system enables amplifier systems that, depending on the specific aspect and intended use, can deliver a high stable gain with near-quantum- limited noise performance, without gain ripples, while also eliminating all reflections of both the signal, the idler and the pump as well as the transmission of all unwanted tones. A further technical effect and advantage is that the amplifier system can isolate, i.e. signals or noise entering at a specific signal output port exit at a predetermined port that is coupled with a termination resistor. The disclosed amplifier system can be made to work when each TWPA is configured to perform three-wave mixing, 3WM, and / or four- wave mixing, 4WM. An additional technical effect and advantage is that the amplifier system reduces pump leakage due to non-idealities, i.e. imperfections, of pump couplers, such as diplexers and directional couplers.

[0011] According to some aspects, the at least two travelling wave parametric amplifiers comprises at least four travelling wave parametric amplifiers. Using four TWPAs enables both the reflected and the transmitted idler to be filtered out by coupling the TWPAs in a suitable way and setting the pump phases to appropriate values.

[0012] According to some aspects, the first interferometer system comprises a first, a second and a third hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. The at least one an input port of the first interferometer comprises the first and second input ports of the first hybrid coupler. The first output port of the first hybrid coupler is connected to the first input port of the second hybrid coupler. The second output port of the first hybrid coupler is connected to the first input port of the third hybrid coupler. The output ports of the first interferometer system comprise the first and second output ports of the second and third hybrid couplers. According to some aspects, the first, second and third hybrid couplers comprise respective first, second and third ninety-degree hybrid couplers. According to some aspects, the second and third hybrid couplers comprise respective second and third one-hundred-eighty-degree hybrid couplers.

[0013] This provides three degrees of freedom: the phases of the second, third and fourth pumps in relation to the first. Consider an example where we want to have the pump phase of the third pump to be the same as the phase of the first pump, while the phases of the second and fourth pumps shifted by one-hundred-and-eighty degrees with respect to the first pump phase. If using said ninety-degree hybrid couplers, we can generate the pump phases using four different phase locked signal sources and setting the phases manually; the same effect can be achieved by using said one-hundred-eighty- degree hybrid couplers.

[0014] According to some aspects, the first interferometer system further comprises a fourth hybrid coupler. The first output port of the fourth hybrid coupler is connected to the second input port of the second hybrid coupler. The second output port of the fourth hybrid coupler is connected to the second input port of the third hybrid coupler. The at least one an input port of the first interferometer system comprises the first and second input ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler of the first interferometer system comprises a one-hundred-eighty-degree hybrid coupler.

[0015] The fourth hybrid coupler, when connected as stated above, in particular when comprising a one-hundred-eighty-degree hybrid coupler, the fourth hybrid coupler can act synergistically with the rest of the amplifier system to eliminate the need for diplexers; it the amplifier system can be configured to separate the three waves of the signal, idler and pump from each other.

[0016] According to some aspects, the second interferometer system comprises a first, a second and a third hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. The at least one input port per TWPA of the second interferometer comprises the first and second input ports of the second and third hybrid couplers. The second output port of the second hybrid coupler is connected to the first input port of the first hybrid coupler. The second output port of the third hybrid coupler is connected to the second input port of the first hybrid coupler. The at least one output port of the second interferometer system comprises the first and second output ports of the first hybrid coupler. According to some aspects, the first, second and third hybrid couplers of the second interferometer system comprise respective first, second and third ninety-degree hybrid couplers. According to some aspects, the second and third hybrid couplers of the second interferometer system comprise respective second and third one-hundred-eighty-degree hybrid couplers. This enables amplifier system configurations that can catch idler reflections in termination resistors of the first interferometer system, while simultaneously guide signals input to the first interferometer system to exit through the first and second output port of the first hybrid coupler, as desired. By further connecting termination resistors to suitable configurations of input and / or output ports of hybrid couplers, at least the following technical effects and advantages can be achieved: the amplifier system can be configured to not reflect any signal or either, as well as not transmitting any idler; the amplifier system can be configured to remove signal and idler reflections such that we get two amplifiers in one; the amplifier system can be configured to amplify in one direction and isolate in the other direction, and a user can choose which direction, by pumping on either pump input ports or pump output ports, with the added effect of not reflecting any idler, thereby making the amplifier system more suitable for sensitive samples.

[0017] According to some aspects, the second interferometer system further comprises a fourth hybrid coupler. The first output port of the second hybrid coupler is connected to the first input port of the fourth hybrid coupler. The first output port of the third hybrid coupler is connected to the second input port of the fourth hybrid coupler. The at least one output port of the second interferometer system comprises the first and second output ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler comprises a one-hundred-eighty-degree hybrid coupler.

[0018] This enables an improved separation of outgoing signal, idler and pump signal.

[0019] According to some aspects, the second interferometer system further comprises a narrowband ninety-degree phase shifter configured to add a ninety-degree phase shift to the pump signal at the connection between the first output port of the third hybrid coupler and the second input port of the fourth hybrid coupler. According to some aspects, the connection between the first output port of the third hybrid coupler of the second interferometer system to the second input port of the fourth hybrid coupler of the second interferometer system is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection. A technical effect and advantage are that this enable separation of the signal, idler and pump outputs. According to some aspects, the at least one input port of the first interferometer system comprises at least two input ports. At least one of said at least two input ports is coupled with a termination resistor. According to some aspects, the at least one output port of the second interferometer system comprises at least two output ports and wherein at least one of said at least two output ports is coupled with a termination resistor. According to some aspects, the first interferometer system and / or the second interferometer system comprises at least one hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. One of the input or output ports of at least one of the at least one hybrid couplers is coupled with a termination resistor. The termination resistors enable a received signal to dissipate if impedance matched. For instance, for transmission lines or wave guides having a fifty Ohm impedance, a fifty Ohm termination resistor will effectively allow an incoming signal to dissipate; the termination resistor will appear as an infinitely long transmission line or wave guide to the incoming signal.

[0020] According to some aspects, each TWPA is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1a illustrates aspects of an amplifier system according to the present disclosure;

[0023] Figure 1 b illustrates aspects of an amplifier system according to the present disclosure;

[0024] Figure 1c illustrates aspects of an amplifier system according to the present disclosure;

[0025] Figure 1d illustrates aspects of an amplifier system according to the present disclosure;

[0026] Figure 2a illustrates aspects of an amplifier system according to the present disclosure;

[0027] Figure 2b illustrates a set of hybrid couplers configured to generate a desired set of pump phases;

[0028] Figure 3 illustrates aspects of an amplifier system according to the present disclosure;

[0029] Figure 4a illustrates aspects of an amplifier system according to the present disclosure;

[0030] Figure 4b illustrates aspects of an amplifier system according to the present disclosure;

[0031] Figure 4c illustrates aspects of an amplifier system according to the present disclosure; Figure 4d illustrates aspects of an amplifier system according to the present disclosure;

[0032] Figure 5 illustrates aspects of an amplifier system according to the present disclosure; and

[0033] Figure 6 illustrates aspects of an amplifier system according to the present disclosure.

[0034] DETAILED DESCRIPTION

[0035] Figure 1a illustrates aspects of an amplifier system 100a according to the present disclosure.

[0036] The amplifier system 100a comprises at least two travelling wave parametric amplifiers 110a-b, TWPA. Each TWPA 110a-b comprises an input port 112a-band an output port 114a-b. According to some aspects, the at least two travelling wave parametric amplifiers 110a-b comprising at least four travelling wave parametric amplifiers.

[0037] The amplifier system 100a further comprises a first interferometer system 120. The first interferometer system 120 comprises at least one input port 102a-b, and at least one output port per TWPA 104a-b.

[0038] The amplifier system also comprises a second interferometer system 140. The second interferometer system 140 comprises at least one output port 108a-b, and at least one input port per TWPA 106a-b.

[0039] The input port 112a-b of each TWPA 110a-b is connected to a respective output port 104a-b of the first interferometer system 120. The output port 114a-b of each TWPA 110a-b is connected to a respective input port 106a-b of the second interferometer system 140.

[0040] Said connections, as well as connections involving a pump, as discussed above and below, may include any type of connection suitable for the signal, pump and idler to propagate along, such as transmission lines, wave guides, e.g. superconducting waveguides, hollow waveguides, integrated optical waveguides, fibre optic cable.

[0041] The TWPAs may comprise either kinetic inductance TWPAs, which uses the nonlinear kinetic inductance of a superconducting transmission line, and / or Josephson TWPAs, which uses the nonlinear inductance of a Josephson junction. Parametric amplification results from frequency mixing in a nonlinear element, where a strong pump is mixed with the weak signal, causing energy transfer from the pump to the signal and hence amplification.

[0042] There are two main schemes of frequency mixing, namely three-wave mixing, 3WM, and four-wave mixing, 4WM. During 3WM, one photon at the pump frequency cop generates a photon at the signal frequency cos and another photon at an idler frequency coi under the resonance condition cop = cos+coi, whereas during 4WM, two photons at the pump frequency create the signal and the idler photons, i.e. , 2cop = cos +coi.

[0043] According to some aspects, each TWPA 110a-b is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM.

[0044] If present, the choice of pump couplings, as discussed above and below, are preferably determined at least in part based on whether the TWPAs are configured perform 3WM or 4WM. In case the pump couplings comprise diplexers, the diplexers are preferably chosen to comprise low pass-high pass diplexers for 3WM and bandstop-bandpass diplexers for 4WM.

[0045] According to some aspects, the amplifier system 100a additionally comprises a set of pump couplings 130a-d. Each pump coupling is configured to couple a pump tone to at least one of the at least one input port 102a-b of the first interferometer system 120 and / or a respective input port 112a-b of the TWPAs 1 10a-b and / or a respective output port 114a-b of the TWPAs 110a-b and / or at least one output port 108a-b of the second interferometer system 140. According to some aspects, the set of input couplings comprises at least one diplexer. According to some aspects, the set of input couplings comprises at least one directional coupler.

[0046] According to some aspects, the first interferometer system 120 comprises a first, a second and a third hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. The at least one an input port of the first interferometer comprises the first and second input ports of the first hybrid coupler. The first output port of the first hybrid coupler is connected to the first input port of the second hybrid coupler. The second output port of the first hybrid coupler is connected to the first input port of the third hybrid coupler. The output ports of the first interferometer system comprise the first and second output ports of the second and third hybrid couplers. According to some aspects, the first, second and third hybrid couplers comprise respective first, second and third ninety-degree hybrid couplers. According to some aspects, the second and third hybrid couplers comprise respective second and third one- hundred-eighty-degree hybrid couplers.

[0047] According to some aspects, the first interferometer system 120 further comprises a fourth hybrid coupler. The first output port of the fourth hybrid coupler is connected to the second input port of the second hybrid coupler. The second output port of the fourth hybrid coupler is connected to the second input port of the third hybrid coupler. The at least one an input port of the first interferometer system comprises the first and second input ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler of the first interferometer system comprises a one-hundred-eighty-degree hybrid coupler.

[0048] According to some aspects, the second interferometer system comprises a first, a second and a third hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. The at least one input port per TWPA of the second interferometer comprises the first and second input ports of the second and third hybrid couplers. The second output port of the second hybrid coupler is connected to the first input port of the first hybrid coupler. The second output port of the third hybrid coupler is connected to the second input port of the first hybrid coupler. The at least one output port of the second interferometer system comprises the first and second output ports of the first hybrid coupler. According to some aspects, the first, second and third hybrid couplers of the second interferometer system comprise respective first, second and third ninety-degree hybrid couplers. According to some aspects, the second and third hybrid couplers of the second interferometer system comprise respective second and third one-hundred-eighty-degree hybrid couplers.

[0049] According to some aspects, the second interferometer system comprises a fourth hybrid coupler. The first output port of the second hybrid coupler is connected to the first input port of the fourth hybrid coupler. The first output port of the third hybrid coupler is connected to the second input port of the fourth hybrid coupler. The at least one output port of the second interferometer system comprises the first and second output ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler comprises a one-hundred-eighty-degree hybrid coupler. According to some aspects, the second interferometer system further comprises a narrowband ninety-degree phase shifter configured to add a ninety-degree phase shift to the pump signal at the connection between the first output port of the third hybrid coupler and the second input port of the fourth hybrid coupler. According to some aspects, the connection between the first output port of the third hybrid coupler of the second interferometer system to the second input port of the fourth hybrid coupler of the second interferometer system is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection.

[0050] According to some aspects, the at least one input port of the first interferometer system 120 comprises at least two input ports 102a-b, and wherein at least one of said at least two input ports is coupled with a termination resistor. According to some aspects, the at least one output port of the second interferometer system 140 comprises at least two output ports 108a-b, and wherein at least one of said at least two output ports is coupled with a termination resistor. According to some aspects, the first interferometer system 120 and / or the second interferometer system 140 comprises at least one hybrid coupler. Each hybrid coupler has a first and a second input port and a first and a second output port. One of the input or output ports of at least one of the at least one hybrid couplers is coupled with a termination resistor.

[0051] According to some aspects, the pump couplings comprises at least one superconducting pump coupling, such as a superconducting diplexer. According to some aspects, at least one of the hybrid couplers comprises a superconducting hybrid coupler.

[0052] The disclosed amplifier system can be configured deliver a high stable gain with near with near-quantum-limited noise performance, without gain ripples, while also eliminating all reflections of both the signal, the idler and the pump as well as the transmission of unwanted tones. Simulations predict over 20 dB ripple-free near- quantum-limited gain in the band 4-8 GHz with 10 dB isolation for a single amplifier, such as those discussed in relation to Figures 1 b-1 d, and 30 dB isolation for a double amplifier, such as those discussed in relation to Figures 2-6. In other words, the disclosed amplifier system can be configured to achieve wideband idler filtering.

[0053] Figures 1 b-1 d illustrate aspects of the amplifier system comprising two TWPAs. In particular, the aspects illustrate some of the technical effects and advantages that can be achieved when different technical features act synergistically. The TWPAs will be illustrated assuming that they are 3WM TWPAs, which will dictate certain relative pump phases, as described further below; the same principles will apply for TWPAs configured for 4WM, though the relative pump phases may differ from those of the 3WM in order to achieve the same technical effects and advantages.

[0054] Figure 1 b illustrates aspects of the amplifier system upon which the amplifier systems of Figures 1 c and 1 d build.

[0055] The amplifier system 100b comprises a first interferometer system 120. The amplifier system further comprises two travelling wave parametric amplifiers 110a-b. The amplifier system also comprises a second interferometer system 140. The first interferometer system 120 comprises two input ports 102a-b and two output ports 104a-b, one per TWPA. The second interferometer system 140 comprises two output ports 108a-b and two input ports 106a-b, one per TWPA. Each TWPA 110a-b comprises an input port 112a-b and an output port 114a-b. The input port 112a-b of each TWPA 110a-b is connected to a respective output port 104a-b of the first interferometer system 120. The output port 114a-b of each TWPA 110a-b is connected to a respective input port 106a- b of the second interferometer system 140. The amplifier system additionally comprises a set of four pump couplings 130c-f. Two of the pump couplings 130c-d are configured to couple a pump tone to a respective input port 112a-b of the TWPAs 110a-b. The other two pump couplings 130e-f are configured to couple a pump tone to a respective output port 114a-b of the TWPAs 110a-b. According to some aspects, the pump couplings 130c-f comprise respective diplexers. According to some aspects, pump couplings 130c- f comprise at least one directional coupler.

[0056] The first interferometer system 120 comprises a hybrid coupler 141 a. The hybrid coupler 141 a has a first 142a and a second input port 144a and a first 146a and a second output port 148a. The two input ports 102a-b of the first interferometer system 120 comprise the first 142a and second input ports 144a of the hybrid coupler 141 a. The two output ports 104a-b of the first interferometer system 120 comprise the first 146a and second input ports 148a of the hybrid coupler 141 a.

[0057] The second interferometer system 140 comprises a hybrid coupler 141 b. The hybrid coupler 141 b has a first 142b and a second input port 144b and a first 146b and a second output port 148b. The two input ports 106a-b of the second interferometer system 140 comprise the first 142b and second input ports 144b of the hybrid coupler 141 b. The two output ports 108a-b of the second interferometer system 140 comprise the first 146b and second input ports 148b of the hybrid coupler 141 b.

[0058] Each hybrid coupler 141 a, 141 b comprises a ninety-degree hybrid coupler.

[0059] The second input port 102b of the first interferometer system 120 is coupled with a termination resistor 150a.

[0060] According to some aspects, each TWPA 110a-b is configured to perform three-wave mixing, 3WM.

[0061] Consider a use case where a user has two pumps, PUMP1 and PLIMP2, operating across respective TWPAs. Input from PLIMP1 is received via pump coupling 130c and output via pump coupling 130e. Input from PLIMP2 is received via pump coupling 130d and output via pump coupling 130f .

[0062] By setting the pump phase between pumps PLIMP1 and PLIMP2 we can get several different technical effects and advantages; assuming 3WM TWPAs, we get:

[0063] If the phase difference is zero radians, the amplifier system will filter out the transmitted idler signal.

[0064] If the phase difference is pi / 2 radians, the amplifier system will filter out the reflected pump leakage.

[0065] If the phase difference is pi radians, the amplifier will filter out the reflected idler.

[0066] If the phase difference is 3*pi / 2 radians, the amplifier system will filter out the transmitted pump leakage.

[0067] The same principle holds if the TWPAs are configured to perform 4WM, but the relative phases may differ from a corresponding 3WM scenario.

[0068] Figure 1 c illustrates aspects of the amplifier systems extending those illustrated in Figure 1 b. Starting from the amplifier system of Figure 1 b, each pump coupling 130e, 130f following a TWPA is coupled with a termination resistor 150c, 150d. Additionally, the second output port 108b of the second interferometer system 140 is coupled with a termination resistor 150b. When using a phase difference of pi radians, the amplifier system reflects neither signal nor idler, which is very useful for people who are doing measurements on very sensitive samples.

[0069] Figure 1 d illustrates aspects of the amplifier systems extending those illustrated in Figure 1 b. Starting from the amplifier system of Figure 1 b, the first output port 108a of the second interferometer system 140 is coupled with a termination resistor 150b.

[0070] When using a phase difference of zero radians, the amplifier system amplifies in one direction and isolates in the other direction. Which direction that is being amplified and which is being isolated can be determined by the user by either pumping the pump couplings 130c, 130d between the first interferometer system 120 and the TWPAs or the pump couplings 130e, 130f, between the second interferometer system 140 and the TWPAs.

[0071] Figure 2a illustrates aspects of an amplifier system 200 comprising at least four TWPAs. The amplifier system 200 comprises a first interferometer system 220. The system further comprises at least four travelling wave parametric amplifiers 210a-d. According to some aspects, each TWPA 210a-d is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM. The system also comprises a second interferometer system 240. The first interferometer system 220 comprises at least one input port 202a- b, and at least one output port 204a-d per TWPA. The second interferometer system 240 comprises at least one output port 208a-b, and at least one input port 206a-d per TWPA. Each TWPA 210a-d comprises an input port 212a-d and an output port 214a-d. The input port 212a-d of each TWPA 210a-d is connected to a respective output port 204a-d of the first interferometer system 220. The output port 214a-d of each TWPA 210a-d is connected to a respective input port 206a-d of the second interferometer system 240.

[0072] According to some aspects, the amplifier system 200 additionally comprises a set of pump couplings 230a-l. Each pump coupling is configured to couple a pump tone to at least one of the at least one input port 202a-b of the first interferometer system 220 and / or a respective input port 212a-d of the TWPAs 210a-d and / or a respective output port 214a-d of the TWPAs 210a-d and / or at least one of the at least one output port 208a-b of the second interferometer system 240. This enables additional technical effects and advantages with respect to amplifier systems only using two TWPA, such as those discussed in relation to Figures 1 b-d; specifically, with the proper relative phases of pump signals, the amplifier system enables eliminating signal and idler reflections, as well as idler output. Another technical effect and advantage is that the amplifier system enables dual parallel amplification without signal reflections or idler reflections, while allowing the output signal and idler to be directed to separate output ports. Yet another technical effect and advantage is that the amplifier system enables amplification in one direction and isolation in the other direction, the amplification and isolation direction being determined by a user of the amplifier system, while also eliminating idler reflections. Aspects illustrating how these technical effects and advantages can be achieved will be further illustrated in relation to Figures 4a-d, below.

[0073] According to some aspects, the first interferometer system 220 comprises a first 241 a, a second 241 b and a third hybrid coupler 241 c. Each hybrid coupler 241 a-c has a first 242a-c and a second input port 244a-c and a first 246a-c and a second output port 248a- c. The at least one an input port 202a-b of the first interferometer 220 comprises the first 242a and second input ports 244a of the first hybrid coupler 241 a. The first output port 246a of the first hybrid coupler 241 a is connected to the first input port 242b of the second hybrid coupler 241 b. The second output port 248a of the first hybrid coupler 241 a being connected to the first input port 242c of the third hybrid coupler 241c. The output ports 204a-d of the first interferometer system 220 comprise the first and second output ports of the second 241 b and third hybrid couplers 241 c.

[0074] According to some aspects, the first 241a, second 241 b and third hybrid couplers 241 c comprise respective first, second and third ninety-degree hybrid couplers.

[0075] According to some aspects, the second 241 b and third hybrid couplers 241 c comprise respective second and third one-hundred-eighty-degree hybrid couplers.

[0076] According to some aspects, the first interferometer system 220 further comprises a fourth hybrid coupler, wherein the first output port of the fourth hybrid coupler is connected to the second input port of the second hybrid coupler. The second output port of the fourth hybrid coupler is connected to the second input port of the third hybrid coupler. The at least one an input port of the first interferometer system 220 comprises the first and second input ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler of the first interferometer system 220 comprises a one-hundred- eighty-degree hybrid coupler. According to some aspects, the second interferometer system 240 comprises a first 241 d, a second 241 e and a third hybrid coupler 241 f. Each hybrid coupler 241 d-f has a first 242d-f and a second input port 244d-f and a first 246d-f and a second output port 248d-f. The at least one input port 206a-d per TWPA of the second interferometer 240 comprises the first 242e-f and second input ports 244e-f of the second 241 e and third hybrid couplers 241 f. The second output port 248e of the second hybrid coupler 241 e is connected to the first input port 242d of the first hybrid coupler 241 d. The second output port 248f of the third hybrid coupler 241 f is connected to the second input port 244d of the first hybrid coupler 241 d. The at least one output port 208a-b of the second interferometer system 240 comprises the first 246d and second output ports 248d of the first hybrid coupler 241 d.

[0077] According to some aspects, the first 241 d, second 241 e and third hybrid couplers 241 f of the second interferometer system 240 comprise respective first, second and third ninety-degree hybrid couplers.

[0078] According to some aspects, the second 241 e and third hybrid couplers 241 f of the second interferometer system 240 comprise respective second and third one-hundred- eighty-degree hybrid couplers.

[0079] According to some aspects, the second interferometer system 240 further comprises a fourth hybrid coupler. The first output port of the second hybrid coupler is connected to the first input port of the fourth hybrid coupler. The first output port of the third hybrid coupler is connected to the second input port of the fourth hybrid coupler. The at least one output port 208a-b of the second interferometer system 240 comprises the first and second output ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler comprises a one-hundred-eighty-degree hybrid coupler. According to some further aspects, the second interferometer system 240 further comprises a narrowband ninety-degree phase shifter configured to add a ninety-degree phase shift to the pump signal at the connection between the first output port of the third hybrid coupler and the second input port of the fourth hybrid coupler. According to some further aspects, the connection between the first output port of the third hybrid coupler of the second interferometer system 240 to the second input port of the fourth hybrid coupler of the second interferometer system 240 is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection.

[0080] According to some aspects, the at least one input port of the first interferometer system 220 comprises at least two input ports 202a-b. At least one of said at least two input ports 202a-b is coupled with a termination resistor.

[0081] According to some aspects, the at least one output port of the second interferometer system 240 comprises at least two output ports 208a-b. At least one of said at least two output ports is coupled with a termination resistor.

[0082] According to some aspects, the first interferometer system 220 and / or the second interferometer system 240 comprises at least one hybrid coupler, each hybrid coupler having a first and a second input port and a first and a second output port, and wherein one of the input or output ports of at least one of the at least one hybrid couplers is coupled with a termination resistor 250a-d.

[0083] Preferred pump phases when operating the amplifier system depends on what a user wants to achieve in combination with the specific aspect of the disclosed amplifier system the user is operating. For example, pump phases can be configured to only filter out the idler or idler and pump leakage.

[0084] If the TWPAs are configured for 3WM and the amplifier system 200 is corresponding to the amplifier system as illustrated in relation to Figure 4a, and with a first set of pump couplings 230c-f and second set of pump couplings 230g-j being configured to eliminate pump leakage, pump phases of zero, pi, zero, pi, across respective first set pump (input) couplings - second set pump (output) couplings will filter out the idler. If instead the TWPAs are configured for 4WM, pump phases of zero, pi / 2, zero, pi / 2 can be used for the same technical effect.

[0085] If the pump couplings experience pump leakage, the pump phases can instead be chosen to minimise leakage. For an amplifier system as illustrated in relation to Figure 4a, setting phases to zero, pi / 2, pi, 3*pi / 2 will filter out reflected pump leakage and reflected idler.

[0086] While pump phases can be generated manually, e.g. using (four) different phase-locked signal sources, it may be more convenient to use three one-hundred-and-eighty-degree hybrid couplers to split a pump signal into four with appropriate pump phases. An aspect of this is illustrated in Figure 2b. Figure 2b illustrate a pump coupling system comprising first, second and third one-hundred-and-eighty-degree hybrid couplers 241 g-241 i. Each hybrid coupler 241 g-241 i comprises two input ports and two output ports. The first output port of the first hybrid coupler 241 g is connected to the second input port of the second hybrid coupler 241 h. The second output port of the first hybrid coupler is connected to the second input port of the third hybrid coupler. Remaining input ports are connected to respective termination resistors 250e-g. The pump coupling system is thus configured to receive a pump (input) signal at pump coupling 230m and output four pump signals at pump couplings 230n-q, with phases zero, pi, zero, pi. The pump coupling system can also be run in reverse. In other words, the pump coupling system is further configured to receive respective pump (output) signals at pump couplings 230n-q and output a combined pump signal at pump coupling 230m.

[0087] Thus, according to some aspects, the amplifier system further comprises two pump coupling systems, one with its four pump couplings 230n-q connected to the first set of pump couplings 230c-f of Figure 2 (or corresponding set of pump couplings for any of the four TWPA aspects discussed above and below), and the other connected to the second set of pump couplings 230g-j, the pump signals to each TWPA will have the phases zero, pi, zero, pi.

[0088] Figure 3 illustrates aspects of an amplifier system 300 comprising at least four TWPAs. In particular, Figure 3 illustrates further extensions of the amplifier systems of Figure 2. The amplifier system 300 comprises a first interferometer system 320. The system further comprises at least four travelling wave parametric amplifiers 310a-d. According to some aspects, each TWPA 310a-d is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM. The system also comprises a second interferometer system 340. The first interferometer system 320 comprises at least one input port 302a- b, and at least one output port 304a-d per TWPA. The second interferometer system 340 comprises at least one output port 308a-d, and at least one input port 306a-d per TWPA. Each TWPA 310a-d comprises an input port 312a-d and an output port 314a-d. The input port 312a-d of each TWPA 310a-d is connected to a respective output port 304a-d of the first interferometer system 320. The output port 314a-d of each TWPA 310a-d is connected to a respective input port 306a-d of the second interferometer system 340. According to some aspects, the amplifier system 300 additionally comprises a set of pump couplings 330a-p. Each pump coupling is configured to couple a pump tone to at least one of the at least one input port 302a-d of the first interferometer system 320 and / or a respective input port 312a-d of the TWPAs 310a-d and / or a respective output port 314a-d of the TWPAs 31 Oa-d and / or at least one of the at least one output port 308a-b of the second interferometer system 340. The technical effects and advantages discussed in relation to Figure 2 applies to the amplifier system 300 of Figure 3 as well.

[0089] According to some aspects, the first interferometer system 320 comprises a first 341 a, a second 341 b and a third hybrid coupler 341 c. Each hybrid coupler 341 a-c has a first 342a-c and a second input port 344a-c and a first 346a-c and a second output port 348a- c. The at least one an input port 302a-d of the first interferometer 320 comprises the first 342a and second input ports 344a of the first hybrid coupler 341 a. The first output port 346a of the first hybrid coupler 341 a is connected to the first input port 342b of the second hybrid coupler 341 b. The second output port 348a of the first hybrid coupler 341 a being connected to the first input port 342c of the third hybrid coupler 341 c. The output ports 304a-d of the first interferometer system 320 comprise the first and second output ports of the second 341 b and third hybrid couplers 341 c.

[0090] According to some aspects, the first 341 a, second 341 b and third hybrid couplers 341c comprise respective first, second and third ninety-degree hybrid couplers.

[0091] According to some aspects, the second 341 b and third hybrid couplers 341 c comprise respective second and third one-hundred-eighty-degree hybrid couplers.

[0092] According to some aspects, the first interferometer system 320 further comprises a fourth hybrid coupler, wherein the first output port of the fourth hybrid coupler is connected to the second input port of the second hybrid coupler. The second output port of the fourth hybrid coupler is connected to the second input port of the third hybrid coupler. The at least one an input port of the first interferometer system 320 comprises the first and second input ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler of the first interferometer system 320 comprises a one-hundred- eighty-degree hybrid coupler.

[0093] According to some aspects, the second interferometer system 340 comprises a first 341 d, a second 341 e and a third hybrid coupler 341 f. Each hybrid coupler 341 d-f has a first 342d-f and a second input port 344d-f and a first 346d-f and a second output port 348d-f. The at least one input port 306a-d per TWPA of the second interferometer 340 comprises the first 342e-f and second input ports 344e-f of the second 341 e and third hybrid couplers 341 f. The second output port 348e of the second hybrid coupler 341 e is connected to the first input port 342d of the first hybrid coupler 341 d. The second output port 348f of the third hybrid coupler 341 f is connected to the second input port 344d of the first hybrid coupler 341 d. The at least one output port 308a-b of the second interferometer system 340 comprises the first 346d and second output ports 348d of the first hybrid coupler 341 d.

[0094] According to some aspects, the first 341 d, second 341 e and third hybrid couplers 341 f of the second interferometer system 340 comprise respective first, second and third ninety-degree hybrid couplers.

[0095] According to some aspects, the second 341 e and third hybrid couplers 341 f of the second interferometer system 340 comprise respective second and third one-hundred- eighty-degree hybrid couplers.

[0096] According to some aspects, the second interferometer system 340 further comprises a fourth hybrid coupler. The first output port of the second hybrid coupler is connected to the first input port of the fourth hybrid coupler. The first output port of the third hybrid coupler is connected to the second input port of the fourth hybrid coupler. The at least one output port 308a-d of the second interferometer system 340 comprises the first and second output ports of the fourth hybrid coupler. According to some aspects, the fourth hybrid coupler comprises a one-hundred-eighty-degree hybrid coupler. According to some further aspects, the second interferometer system 340 further comprises a narrowband ninety-degree phase shifter configured to add a ninety-degree phase shift to the pump signal at the connection between the first output port of the third hybrid coupler and the second input port of the fourth hybrid coupler. According to some further aspects, the connection between the first output port of the third hybrid coupler of the second interferometer system 340 to the second input port of the fourth hybrid coupler of the second interferometer system 340 is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection. According to some aspects, the at least one input port of the first interferometer system 320 comprises at least two input ports 302a-d. At least one of said at least two input ports 302a-d is coupled with a termination resistor.

[0097] According to some aspects, the at least one output port of the second interferometer system 340 comprises at least two output ports 308a-d. At least one of said at least two output ports is coupled with a termination resistor.

[0098] According to some aspects, the first interferometer system 320 and / or the second interferometer system 340 comprises at least one hybrid coupler, each hybrid coupler having a first and a second input port and a first and a second output port, and wherein one of the input or output ports of at least one of the at least one hybrid couplers is coupled with a termination resistor.

[0099] In relation to Figure 2a above and Figures 4a-4d below, examples of how specific choices of pump phases result in different types of technical effects for different aspects of the disclosed amplifier system. Here we provide examples of preferred pump phases when the amplifier system is configured as illustrated in relation to Figure 6, with each TWPA 310a-d being configured for 3WM. If a user inputs the signal via the first input port 302a, corresponding to 602a in Figure 6, and the pump via the third input port 302c, corresponding to 602c in Figure 6, the ninety- 341 a, 341 d and one-hundred-and-eighty- degree hybrid couplers 341 b-c, 341 e-h, when connected as illustrated in relation to Figure 6, will cause phase shifts that separates the signal, idler and pump to respective output ports 308b-d of the amplifier system.

[0100] Figures 4a-4d illustrate specific sets of aspects aimed at further illustrating how desired technical effects and advantages discussed in relation to Figures 2 and 3 may be obtained.

[0101] Figure 4a illustrates an aspect of an amplifier system 400a comprising a first interferometer system 420. The amplifier system further comprises at least four travelling wave parametric amplifiers 410a-d. According to some aspects, wherein each TWPA 410a-d is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM. The amplifier system also comprises a second interferometer system 440. The first interferometer system 420 comprises two input ports 402a-b, and at least one output port per TWPA 404a-d. The second interferometer system 440 comprises two output ports 408a-b, and at least one input port per TWPA 406a-d. Each TWPA 410a-d comprises an input port 412a-d and an output port 414a-d. The input port 412a-d of each TWPA 41 Oa-d is connected to a respective output port 404a-d of the first interferometer system 420. The output port 414a-d of each TWPA 41 Oa-d is connected to a respective input port 406a-d of the second interferometer system 440. The amplifier system further comprises a first 430a-d and a second set of pump couplings 430e-h. The first set of pump couplings 430a-d is configured to couple a pump tone to a respective input port 412a-d of the TWPAs 41 Oa-d. The second set of pump couplings 430e-h is configured to couple a pump tone to a respective output port 414a-d of the TWPAs 41 Oa-d.

[0102] The first interferometer system 420 comprises a first 441a, a second 441 b and a third hybrid coupler 441 c. Each hybrid coupler 441 a-c has a first 442a-c and a second input port 444a-c and a first 446a-c and a second output port 448a-c. The two input ports 402a-b of the first interferometer 420 comprise the first 442a and second input ports 444a of the first hybrid coupler 441a. The first output port 446a of the first hybrid coupler 441 a is connected to the first input port 442b of the second hybrid coupler 441 b. The second output port 448a of the first hybrid coupler 441 a is connected to the first input port 442c of the third hybrid coupler 441 c. The output ports 404a-d of the first interferometer system 420 comprise the first and second output ports of the second 441 b and third hybrid couplers 441 c.

[0103] The first 441a, second 441 b and third hybrid couplers 441 c of the first interferometer system 420 comprise respective first, second and third ninety-degree hybrid couplers.

[0104] The second input port 444b of the second hybrid coupler 441 b of the first interferometer system 420 is coupled with a termination resistor 450a. The second input port 444c of the third hybrid coupler 441 c of the first interferometer system 420 is coupled with a termination resistor 450b.

[0105] The second interferometer system 440 comprises a first 441 d, a second 441 e and a third hybrid coupler 441f. Each hybrid coupler 441 d-f has a first 442d-f and a second input port 444d-f and a first 446d-f and a second output port 448d-f. The at least one input port 406a-d per TWPA of the second interferometer 440 comprise the first 442e-f and second input ports 444e-f of the second 441 e and third hybrid couplers 441f. The second output port 448e of the second hybrid coupler 441 e is connected to the first input port 442d of the first hybrid coupler 441 d. The second output port 448f of the third hybrid coupler 441 f is connected to the second input port 444d of the first hybrid coupler 441 d. The two output ports 408a-b of the second interferometer system 440 comprise the first 446d and second output ports 448d of the first hybrid coupler 441 d.

[0106] The first 441 d, second 441 e and third hybrid couplers 441 f of the second interferometer system 440 comprise respective first, second and third ninety-degree hybrid couplers.

[0107] The first output port 446e of the second hybrid coupler 441 e of the second interferometer system 440 is coupled with a termination resistor 450c. The first output port 446f of the third hybrid coupler 441 f of the second interferometer system 440 is coupled with a termination resistor 450d.

[0108] The technical effects and advantages will be discussed under the assumption that the TWPAs are configured to perform three-wave mixing, 3WM, but the same approach applies for 4WM as well.

[0109] Consider a user applying four pump tones, PUMP1 -PUMP4, via the pump couplings 430a-h; specifically, consider the case when pump couplings 430a and 430e are used for PLIMP1 in and out respectively, pump couplings 430b and 430f are used for PLIMP2 in and out respectively, pump couplings 430c and 430g are used for PLIMP3 in and out respectively, and pump couplings 430d and 430h are used for PLIMP4 in and out respectively. By setting the relative phases of PLIMP1 to PLIMP4 to zero, pi, zero, pi radians, respectively the following technical effects and advantages are achieved: idler reflections will be caught in the termination resistors 450a, 450b in the first interferometer system 420; at the same time, the idler generated by a signal from the first input port 402a of the first interferometer system 420 will exit through the first output port 408a of the second interferometer system 440, and the idler generated by a signal from the second input port 402b of the first interferometer system 420 will exit through the second output port 408b of the second interferometer system 440.

[0110] The aspects disclosed in relation to Figures 4b-d build on the amplifier system illustrated in relation to Figure 4a.

[0111] Figure 4b illustrates an amplifier system like that illustrated in relation to Figure 4a, above, wherein the second input port 402b of the first interferometer system 420 and the first output port 408a of the second interferometer system 440 are coupled with respective termination resistors 450e and 450f. When used with the same pump setup as in Figure 4a, technical effects and advantages include: the amplifier system 400 does not reflect any signal, nor any idler, as well as not transmitting any idler.

[0112] Figure 4c illustrates an amplifier system like that illustrated in relation to Figure 4a, above, wherein the second set of pump couplings 430e-h are coupled with respective termination resistors 450e-h.

[0113] When used with the same pump setup as in Figure 4a, technical effects and advantages include: the amplifier system 400 acts as two amplifiers in one, neither one having any reflections of the signal or the idler; the two amplifiers transmit the idler and the signal into different channels.

[0114] Since the resulting idler does not go in the same channel as the signal, several amplifiers can be chained. Thus, according to some aspects, each output port of the second interferometer system is coupled to a respective input port of a first interferometer system of a respective amplifier system as described in relation to Figure 4b.

[0115] Figure 4d illustrates an amplifier system like that illustrated in relation to Figure 4a, above, wherein the second input port 402b of the first interferometer system 420 and the second output port 408b of the second interferometer system 440 are coupled with respective termination resistors 450e and 450f.

[0116] When used with the same pump setup as in Figure 4a, technical effects and advantages include: the amplifier system 400 amplifies in one direction and isolates in the other direction, wherein the direction can be chosen by pumping either the first 430a-d or the second set 430e-h of pump couplings, while not reflecting any idler, which is suitable for sensitive samples.

[0117] According to some aspects, the second set of pump couplings 430e-h are coupled with respective termination resistors. If the TWPAs are configured for 3WM, this results in an amplifier system where one can read out the signal at the idler frequency, coi = cop - cos. A further technical effect is that the amplifier system also isolates.

[0118] Two amplifier systems as illustrated in Figure 4d can also be connected in series. According to some aspects, the first output port 408a of the second interferometer system 440 of a first amplifier system 400 is connected to a first input port 402a of a first interferometer system 420 of a second amplifier system 400. Additionally, each pump coupling of the second set of pump couplings of the first amplifier system is connected a respective pump coupling of the first set of pump couplings of the second amplifier system. The resulting amplifier system improves isolation without sacrificing any gain of significance. A further technical effect is that the initial signal frequency, i.e. the input signal to the first amplifier system, can be retrieved.

[0119] Figure 5 illustrates specific aspects of the amplifier system described in relation to Figure 2. Among other things, the aspects Figure 5 will illustrate how synergistic effects can be achieved when the first and second interferometers comprise both ninety-degree and one-hundred-and-eighty-degree hybrid couplers.

[0120] Figure 5 illustrates an aspect of an amplifier system 500 comprising a first interferometer system 520. The amplifier system further comprises at least four travelling wave parametric amplifiers 510a-d. According to some aspects, wherein each TWPA 510a-d is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM. The amplifier system also comprises a second interferometer system 540. The first interferometer system 520 comprises two input ports 502a-b, and at least one output port per TWPA 504a-d. The second interferometer system 540 comprises four output ports 508a-d, and at least one input port per TWPA 506a-d. Each TWPA 510a-d comprises an input port 512a-d and an output port 514a-d. The input port 512a-d of each TWPA 510a-d is connected to a respective output port 504a-d of the first interferometer system 520. The output port 514a-d of each TWPA 510a-d is connected to a respective input port 506a-d of the second interferometer system 540. The amplifier system 500 further comprises a first 530a-d and a second set of pump couplings 530e-h. The first set of pump couplings 530a-d is configured to couple a pump tone to a respective input port 512a-d of the TWPAs 510a-d. The second set of pump couplings 530e-h is configured to couple a pump tone to a respective output port 514a-d of the TWPAs 510a- d.

[0121] The first interferometer system 520 comprises a first 541 a, a second 541 b and a third hybrid coupler 541 c. Each hybrid coupler 541 a-c has a first 542a-c and a second input port 544a-c and a first 546a-c and a second output port 548a-c. The two input ports 502a-b of the first interferometer 520 comprise the first 542a and second input ports 544a of the first hybrid coupler 541 a. The first output port 546a of the first hybrid coupler 541 a is connected to the first input port 542b of the second hybrid coupler 541 b. The second output port 548a of the first hybrid coupler 541 a is connected to the first input port 542c of the third hybrid coupler 541c. The output ports 504a-d of the first interferometer system 520 comprise the first and second output ports of the second 541 b and third hybrid couplers 541 c.

[0122] The second input port 544b of the second hybrid coupler 541 b of the first interferometer system 520 is coupled with a termination resistor 550b. The second input port 544c of the third hybrid coupler 541c of the first interferometer system 520 is coupled with a termination resistor 550b.

[0123] The second input port 502b of the first interferometer system 520 is coupled with a termination resistor 550a.

[0124] The second interferometer system 540 comprises a first 541 d, a second 541 e and a third hybrid coupler 541f. Each hybrid coupler 541 d-f has a first 542d-f and a second input port 544d-f and a first 546d-f and a second output port 548d-f. The at least one input port 506a-d per TWPA of the second interferometer 540 comprise the first 542e-f and second input ports 544e-f of the second 541 e and third hybrid couplers 541f. The second output port 548e of the second hybrid coupler 541 e is connected to the first input port 542d of the first hybrid coupler 541 d. The second output port 548f of the third hybrid coupler 541f is connected to the second input port 544d of the first hybrid coupler 541 d. The output ports 508a-d of the second interferometer system 540 comprise the first 546d and second output ports 548d of the first hybrid coupler 541 d.

[0125] An output port 508a of the second interferometer system 540 comprising the first output port 546d of the first hybrid coupler 541 d of the second interferometer system 540 is coupled with a termination resistor 550d.

[0126] The second interferometer system 540 further comprises a fourth hybrid coupler 541 g. The first output port 546e of the second hybrid coupler 541 e is connected to the first input port 542g of the fourth hybrid coupler 541 g. The first output port 546f of the third hybrid coupler 541 f is connected to the second input port 544g of the fourth hybrid coupler 541 g. The output ports 508a-d of the second interferometer system 540 comprises the first 546g and second output ports 548g of the fourth hybrid coupler 541g. An output port 508d of the second interferometer system 540 comprising the second output port 548g of the fourth hybrid coupler 541 g of the second interferometer system 540 is coupled with a termination resistor 550e.

[0127] According to some aspects, the first hybrid coupler 541 a of the first interferometer system 520 and first 541 d and fourth 541 g hybrid couplers of the second interferometer system 540 each comprise a ninety-degree hybrid coupler. According to some further aspects, the second 541 b and third 541 c hybrid couplers of the first interferometer system 520 and the second 541 e and third 541 f hybrid couplers of the second interferometer system 540 each comprise a one-hundred-and-eighty-degree hybrid coupler. The pump can then be separated from the signal and the idler by adding a phase shift before the last hybrid coupler the pump encounters. Thus, according to some aspects, the second interferometer system 540 further comprises a narrowband ninetydegree phase shifter 543 configured to add a ninety-degree phase shift to the pump signal at the connection 545 between the first output port 546f of the third hybrid coupler 541 f and the second input port 544g of the fourth hybrid coupler. A convenient choice to obtain the ninety-degree phase shift is to have the connection 545 comprise a quarterwave transmission line or wave guide at the pump frequency. In other words, according to some aspects, the connection 545 between the first output port 546f of the third hybrid coupler 541 f of the second interferometer system 540 to the second input port 544g of the fourth hybrid coupler 541 g of the second interferometer system 540 is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection 545.

[0128] Figure 6 illustrates aspects of the disclosed amplifier system. In particular, Figure 6 illustrates how the amplifier system of Figure 5 can be modified to reduce the number of pump couplings needed. By appropriately adding another one-hundred-and-eighty- degree hybrid coupler to the first interferometer system, the first and second sets of pump couplings can be removed, as will be described further below.

[0129] Figure 6 illustrates an aspect of an amplifier system 600 comprising a first interferometer system 620. The amplifier system 600 further comprises at least four travelling wave parametric amplifiers 610a-d. According to some aspects, each TWPA 610a-d is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM. The amplifier system also comprises a second interferometer system 640. The first interferometer system 620 comprises four input ports 602a-d, and at least one output port per TWPA 604a-d. The second interferometer system 640 comprises four output ports 608a-d, and at least one input port per TWPA 606a-d. Each TWPA 610a-d comprises an input port 612a-d and an output port 614a-d. The input port 612a-d of each TWPA 610a-d is connected to a respective output port 604a-d of the first interferometer system 620. The output port 614a-d of each TWPA 610a-d is connected to a respective input port 606a-d of the second interferometer system 640.

[0130] The first interferometer system 620 comprises a first 641 a, a second 641 b and a third hybrid coupler 641 c. Each hybrid coupler 641 a-c has a first 642a-c and a second input port 644a-c and a first 646a-c and a second output port 648a-c. The input ports 602a-d of the first interferometer 620 comprise the first 642a and second input ports 644a of the first hybrid coupler 641a. The first output port 646a of the first hybrid coupler 641a is connected to the first input port 642b of the second hybrid coupler 641 b. The second output port 648a of the first hybrid coupler 641 a is connected to the first input port 642c of the third hybrid coupler 641 c. The output ports 604a-d of the first interferometer system 620 comprise the first and second output ports of the second 641 b and third hybrid couplers 641c.

[0131] An input port 602b of the first interferometer system 620 comprising the second input port 644a of the first hybrid coupler 641 a of the first interferometer system 620 is coupled with a termination resistor 650a. An input port 602d of the first interferometer system 620 comprising the second input port 644h of the fourth hybrid coupler 641 h of the first interferometer system 620 is coupled with a termination resistor 650b.

[0132] The second interferometer system 640 comprises a first 641 d, a second 641 e and a third hybrid coupler 641f. Each hybrid coupler 641 d-f has a first 642d-f and a second input port 644d-f and a first 646d-f and a second output port 648d-f. The at least one input port 606a-d per TWPA of the second interferometer 640 comprise the first 642e-f and second input ports 644e-f of the second 641 e and third hybrid couplers 641f. The second output port 648e of the second hybrid coupler 641 e is connected to the first input port 642d of the first hybrid coupler 641 d. The second output port 648f of the third hybrid coupler 641 f is connected to the second input port 644d of the first hybrid coupler 641 d. The output ports 608a-d of the second interferometer system 640 comprise the first 646d and second output ports 648d of the first hybrid coupler 641 d.

[0133] An output port 608a of the second interferometer system 640 comprising the first output port 646d of the first hybrid coupler 641 d of the second interferometer system 640 is coupled with a termination resistor 650c.

[0134] The second interferometer system 640 further comprises a fourth hybrid coupler 641 g. The first output port 646e of the second hybrid coupler 641 e is connected to the first input port 642g of the fourth hybrid coupler 641 g. The first output port 646f of the third hybrid coupler 641 f is connected to the second input port 644g of the fourth hybrid coupler 641g. The output ports 608a-d of the second interferometer system 640 comprises the first 646g and second output ports 648g of the fourth hybrid coupler 641 g.

[0135] According to some aspects, an output port 608d of the second interferometer system 640 comprising the second output port 648g of the fourth hybrid coupler 641 g of the second interferometer system 640 is coupled with a termination resistor 650d.

[0136] According to some aspects, the first hybrid coupler 641a of the first interferometer system 620 and first 641 d and fourth 641g hybrid couplers of the second interferometer system 640 each comprise a ninety-degree hybrid coupler. According to some further aspects, the second 641 b, third 641 c and fourth 641 h hybrid couplers of the first interferometer system 620 and the second 641 e and third 641 f hybrid couplers of the second interferometer system 640 each comprise a one-hundred-and-eighty-degree hybrid coupler.

[0137] By pumping an input port 602c, with the signal entering at input port 602a, of the first interferometer system 620 comprising the first input port of the fourth hybrid coupler 642h of the first interferometer system 620, the pump can be separated from the signal and the idler by adding a phase shift before the last hybrid coupler the pump encounters.

[0138] Specifically, the signal, idler and pump out will exit at output ports 608b, 608c, 608d of the second interferometer system 640, respectively. By adding the termination resistor 650d, as described above, the pump out signal will be absorbed by the termination resistor 650d. Thus, according to some aspects, the second interferometer system 640 further comprises a narrowband ninety-degree phase shifter 643 configured to add a ninetydegree phase shift to the pump signal at the connection 645 between the first output port 646f of the third hybrid coupler 641 f and the second input port 644g of the fourth hybrid coupler. A convenient choice to obtain the ninety-degree phase shift is to have the connection 645 comprise a quarter-wave transmission line or wave guide at the pump frequency. In other words, according to some aspects, the connection 645 between the first output port 646f of the third hybrid coupler 641 f of the second interferometer system 640 to the second input port 644g of the fourth hybrid coupler 641g of the second interferometer system 640 is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection 645.

Claims

CLAIMS1. An amplifier system (100a-d, 200, 300, 400a-d, 500, 600) comprising- a first interferometer system (120, 220, 320, 420, 520, 620),- at least four travelling wave parametric amplifiers (110a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d), TWPA,- a second interferometer system (140, 240, 340, 440, 540, 640),- a set of pump couplings (130a-h, 230a-l, 330a-p, 430a-h, 530a-h, 630a-h), the first interferometer system (120, 220, 320, 420, 520, 620) comprising at least one input port (102a-b, 202a-b, 302a-d, 402a-b, 502a-b, 602a-d), and at least one output port per TWPA (104a-b, 204a-d, 304a-d, 404a-d, 504a-d, 604a-d), the second interferometer system (140, 240, 340, 440, 540, 640) comprising at least one output port (108a-b, 208a-b, 308a-d, 408a-b, 508a-d, 608a-d), and at least one input port per TWPA (106a-b, 206a-d, 306a-d, 406a-d, 506a- d, 606a-d), wherein each TWPA (110a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d) comprises an input port (112a-b, 212a-d, 312a-d, 412a-d, 512a-d, 612a-d) and an output port (114a-b, 214a-d, 314a-d, 414a-d, 514a-d, 614a-d), wherein the input port (112a-b, 212a-d, 312a-d, 412a-d, 512a-d, 612a-d) of each TWPA (1 10a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d) is connected to a respective output port (104a-b, 204a-d, 304a-d, 404a-d, 504a-d, 604a-d) of the first interferometer system (120, 220, 320, 420, 520, 620), wherein the output port (114a-b, 214a-d, 314a-d, 414a-d, 514a-d, 614a-d) of each TWPA (1 10a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d) is connected to a respective input port (106a-b, 206a-d, 306a-d, 406a-d, 506a-d, 606a-d) of the second interferometer system (140, 240, 340, 440, 540, 640), wherein each pump coupling being configured to couple a pump tone to at least one of the at least one input port (102a-b, 202a-d, 302a-d, 402a- b, 502a-b, 602a-d) of the first interferometer system (120, 220, 320, 420, 520, 620) and / or a respective input port (112a-b, 212a-d, 312a-d, 412a-d, 512a-d, 612a-d) of the TWPAs (110a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d) and / ora respective output port (114a-b, 214a-d, 314a-d, 414a-d, 514a-d, 614a- d) of the TWPAs (110a-b, 210a-d, 310a-d, 410a-d, 510a-d, 610a-d) and / or at least one output port (108a-b, 208a-b, 308a-d, 408a-b, 508a-d, 608a-d) of the second interferometer system (140, 240, 340, 440, 540, 640), and wherein the amplifier system (100a-d, 200, 300, 400a-d, 500, 600) is configured perform at least one of:• eliminating pump signal reflections and / or idler reflections,• eliminating idler output signal,• dual parallel amplification without pump signal reflections and / or without idler reflections, optionally with the dual parallel amplification directing the pump signal and idler to separate output ports, and• amplification in one direction and isolation in the other direction while eliminating idler reflections, based on a set of predetermined relative phases of the pump tones.

2. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 1 , the first interferometer system (120, 220, 320, 420, 520, 620) comprising a first (241 a, 341 a, 441 a, 541a, 641 a), a second (241 b, 341 b, 441 b, 541 b, 641 b) and a third hybrid coupler (241 c, 341 c, 441c, 541 c, 641 c), each hybrid coupler (241a- c, 341 a-c, 441 a-c, 541 a-c, 641 a-c) having a first (242a-c, 342a-c, 442a-c, 542a- c, 642a-c) and a second input port (244a-c, 344a-c, 444a-c, 544a-c, 644a-c) and a first (246a-c, 346a-c, 446a-c, 546a-c, 646a-c) and a second output port (248a- c, 348a-c, 448a-c, 548a-c, 648a-c), the at least one an input port (102a-b, 202a- b, 302a-d, 402a-b, 502a-b, 602a-d) of the first interferometer (120, 220, 320, 420, 520, 620) comprising the first (242a, 342a, 442a, 542a, 642a) and second input ports (244a, 344a, 444a, 544a, 644a) of the first hybrid coupler (241 a, 341 a, 441 a, 541 a, 641a), the first output port (246a, 346a, 446a, 546a, 646a) of the first hybrid coupler (241 a, 341 a, 441 a, 541 a, 641 a) being connected to the first input port (242b, 342b, 442b, 542b, 642b) of the second hybrid coupler (241 b, 341 b, 441 b, 541 b, 641 b), the second output port (248a, 348a, 448a, 548a, 648a) of the first hybrid coupler (241 a, 341 a, 441a, 541a, 641 a) being connected to the first input port (242c, 342c, 442c, 542c, 642c) of the third hybrid coupler (241 c, 341 c, 441 c, 541 c, 641 c), the output ports (304a-d, 404a-d, 504a-d, 604a-d) of the firstinterferometer system (120, 220, 320, 420, 520, 620) comprising the first and second output ports of the second (241 b, 341 b, 441 b, 541 b, 641 b) and third hybrid couplers (241 c, 341 c, 441 c, 541 c, 641 c).

3. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 2, wherein the first (241 a, 341a, 441a, 541a, 641a), second (241 b, 341 b, 441 b, 541 b, 641 b) and third hybrid couplers (241 c, 341 c, 441 c, 541 c, 641 c) comprise respective first, second and third ninety-degree hybrid couplers.

4. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 2, wherein the second (241 b, 341 b, 441 b, 541 b, 641 b) and third hybrid couplers (241 c, 341 c, 441 c, 541 c, 641 c) comprise respective second and third one- hundred-eighty-degree hybrid couplers.

5. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of claims 2-4, the first interferometer system (120, 220, 320, 420, 520, 620) further comprising a fourth hybrid coupler (341 h, 641 h), wherein the first output port (346h, 646h) of the fourth hybrid coupler is connected to the second input port (344b, 644b) of the second hybrid coupler (341 b, 641 b), wherein the second output port (348h, 648h) of the fourth hybrid coupler (341 h, 641 h) is connected to the second input port (344c, 644c) of the third hybrid coupler (341 c, 641c), and wherein the at least one an input port of the first interferometer system (120, 220, 320, 420, 520, 620) comprises the first (342h, 642h) and second input ports (344h, 644h) of the fourth hybrid coupler (341 h, 641 h).

6. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 5, wherein the fourth hybrid coupler (341 h, 641 h) of the first interferometer system (120, 220, 320, 420, 520, 620) comprises a one-hundred-eighty-degree hybrid coupler.

7. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of claim 2-6, the second interferometer system (140, 240, 340, 440, 540, 640) comprising a first (241 d, 341 d, 441 d, 541 d, 641 d), a second (241 e, 341 e, 441 e, 541 e, 641 e) and a third hybrid coupler (241 f, 341 f, 441 f, 541 f, 641 f), each hybrid coupler (241 d-f, 341 d-f, 441 d-f, 541 d-f, 641 d-f) having a first (242d-f, 342d-f,442d-f, 542d-f, 642d-f) and a second input port (244d-f, 344d-f, 444d-f, 544d-f, 644e-f) and a first (246d-f, 346d-f, 446d-f, 546d-f, 646d-f) and a second output port (248d-f, 348d-f, 448d-f, 548d-f, 648d-f), the at least one input port (106a-b, 206a-d, 306a-d, 406a-d, 506a-d, 606a-d) per TWPA of the second interferometer (140, 240, 340, 440, 540, 640) comprising the first (242e-f, 342e-f, 442e-f, 542e- f, 642e-f) and second input ports (244e-f, 344e-f, 444e-f, 544e-f, 644e-f) of the second (241 e, 341 e, 441 e, 541 e, 641 e) and third hybrid couplers (241 f, 341 f, 441 f, 541 f, 641 f), the second output port (248e, 348e, 448e, 548e, 648e) of the second hybrid coupler (241 e, 341 e, 441 e, 541 e, 641 e) being connected to the first input port (242d, 342d, 442d, 542d, 642d) of the first hybrid coupler (241 d, 341 d, 441 d, 541 d, 641 d), the second output port (248f, 348f, 448f, 548f, 648f) of the third hybrid coupler (241 f, 341 f, 441 f, 541 f, 641 f) being connected to the second input port (244d, 344d, 444d, 544d, 644d) of the first hybrid coupler (241 d, 341 d, 441 d, 541 d, 641 d), the at least one output port (108a-b, 208a-b, 308a-d, 408a-b, 508a-d, 608a-d) of the second interferometer system (140, 240, 340, 440, 540, 640) comprising the first (246d, 346d, 446d, 546d, 646d) and second output ports (248d, 348d, 448d, 548d, 648d) of the first hybrid coupler (241 d, 341 d, 441 d, 541 d, 641 d).

8. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 7, wherein the first (241 d, 341 d, 441 d, 541 d, 641 d), second (241 e, 341 e, 441 e, 541 e, 641 e) and third hybrid couplers (241 f, 341 f, 441 f, 541 f, 641 f) of the second interferometer system (140, 240, 340, 440, 540, 640) comprise respective first, second and third ninety-degree hybrid couplers.

9. The amplifier system (100a-d, 200, 300, 400, 500a-d, 600, 700) according to claim 8, wherein the second (241 e, 341 e, 441 e, 541 e, 641 e) and third hybrid couplers (241 f, 341 f, 441 f, 541 f, 641 f) of the second interferometer system (140, 240, 340, 440, 540, 640) comprise respective second and third one-hundred- eighty-degree hybrid couplers.

10. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of claims 7-9, the second interferometer system (140, 240, 340, 440, 540, 640) further comprising a fourth hybrid coupler (341 g, 541 g, 641g), wherein the firstoutput port (346e, 546e, 646e) of the second hybrid coupler (341 e, 541 e, 641 e) is connected to the first input port (342g, 542g, 642g) of the fourth hybrid coupler (341 g, 541g, 641 g), wherein the first output port (346f, 546f, 646f) of the third hybrid coupler (341 f, 541 f, 641 f) is connected to the second input port (344g, 544g, 644g) of the fourth hybrid coupler (341 g, 541 g, 641 g), and wherein the at least one output port (108a-b, 208a-b, 308a-d, 408a-b, 508a-d, 608a-d) of the second interferometer system (340, 540, 640) comprises the first (346g, 546g, 646g) and second output ports (348g, 548g, 648g) of the fourth hybrid coupler (341 g, 541 g, 641g).11 . The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 10, wherein the fourth hybrid coupler (341 g, 541 g, 641 g) comprises a one-hundred- eighty-degree hybrid coupler.

12. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 10 or 11 , wherein the second interferometer system (140, 240, 340, 440, 540, 640) further comprises a narrowband ninety-degree phase shifter (343, 643) configured to add a ninety-degree phase shift to the pump signal at the connection (345, 645) between the first output port (346f, 646f) of the third hybrid coupler (341 f, 641 f) and the second input port (344g, 644g) of the fourth hybrid coupler (341 g, 641 g).

13. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to claim 11 or 12, wherein the connection (345, 645) between the first output port (346f, 646f) of the third hybrid coupler (341 f, 641 f) of the second interferometer system (140, 240, 340, 440, 540, 640) to the second input port (344g, 644g) of the fourth hybrid coupler (341 g, 641 g) of the second interferometer system (140, 240, 340, 440, 540, 640) is configured to have length corresponding to a quarter of a predetermined pump frequency, the predetermined pump frequency relating to a frequency of a potential pump signal propagating across said connection (345, 645).

14. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of the previous claims, wherein the at least one input port of the first interferometer system (120, 220, 320, 420, 520, 620) comprises at least two input ports (102a-b, 202a-b, 302a-d, 402a-b, 502a-b, 602a-d), and wherein at least one of said at least two input ports (102a-b, 202a-d, 302a-d, 402a-b, 502a-b, 602a-d) is coupled with a termination resistor (150a-d, 250a-d, 450a-h, 550a-e, 650a-d).

15. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of the previous claims, wherein the at least one output port of the second interferometer system (140, 240, 340, 440, 540, 640) comprises at least two output ports (108a-b, 208a-b, 308a-d, 408a-b, 508a-d, 608a-d) and wherein at least one of said at least two output ports is coupled with a termination resistor (150a-d, 250a-d, 450a-h, 550a-e, 650a-d).

16. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of the previous claims, wherein the first interferometer system (120, 220, 320, 420, 520, 620) and / or the second interferometer system (140, 240, 340, 440, 540, 640) comprises at least one hybrid coupler, each hybrid coupler having a first and a second input port and a first and a second output port, and wherein one of the input or output ports of at least one of the at least one hybrid couplers is coupled with a termination resistor (150a-d, 250a-d, 450a-h, 550a-e, 650a-d).

17. The amplifier system (100a-d, 200, 300, 400a-d, 500, 600) according to any of the previous claims, wherein each TWPA (110a-b, 21 Oa-d, 31 Oa-d, 41 Oa-d, 510a- d, 61 Oa-d) is configured to perform three-wave mixing, 3WM, and / or four-wave mixing, 4WM.

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