Microwave signal amplifier with isolation

Abstract

The invention relates to a microwave signal amplifier comprising a chain of nonlinear inductive dipole elements, each forming a superconducting asymmetric loop with Josephson junctions, the chain being arranged between an input of the chain for applying a signal to be amplified and an output of the chain at which an output signal is generated, the amplifier further comprising a controllable magnetic flux generation system for circulating a current in the loops, the amplifier further comprising a first microwave pump and a means for coupling the input of the chain to the first pump, the first pump generating, through the first coupling means, a wave in the chain in the direction from the input towards the output, the frequency of which wave is adjusted in order to transfer power at the frequency of the signal to be amplified. The device further comprises a second microwave pump and a second means for coupling the output of the chain to the second pump, the second pump generating, through the second coupling means, a wave in the chain in the direction from the output towards the input, at a frequency that is different from that of the first pump, so as to attenuate, in said direction from the output towards the input, the microwaves propagating at the frequency of the signal to be amplified.

Description

DESCRIPTION Title of the invention: Microwave signal amplifier with isolation Technical field - technological background

[0001] The invention falls within the field of amplifiers for very weak electromagnetic signals, particularly but not only for quantum computing.

[0002] In particular, the invention falls within the field of circuits transmitting hyperfrequency waves or microwaves. It is a matter of designing and handling these circuits, ensuring that the signals of interest are amplified, that no parasitic signal is generated, and that the ambient noise and the noise of the components used is kept away from the amplification chain or filtered in it, in the direction of amplification but also in the opposite direction, since it is necessary to avoid exposing the signal source to waves which would reach it through the reading chain - then traveled in the opposite direction - and would disturb it. With regard to avoiding the transfer of waves in the opposite direction, we speak of obtaining isolation of the source, and this constitutes a task in itself.

[0003] The circuits considered can be highly integrated circuits. They are based on components with superconducting properties, called superconducting components, which are placed in cryogenic enclosures to benefit from a temperature of at most a few K (a few Kelvins).

[0004] Typically, the superconducting circuit considered is an amplification circuit intended to amplify a microwave wave coming from a qubit or quantum bit, whose state we wish to know. It can alternatively be intended for reading spin magnetic resonance information (in other words electronic paramagnetic resonance), or for amplifying a radio wave of astronomical origin. In all these situations, a very low power microwave is to be amplified.

[0005] In this context, parametric amplifiers are known, based on a medium with non-linear behavior, which allows wave mixing, namely the transfer of energy from one frequency to another. The non-linear behavior is modified by regulating the medium, in order to obtain the phase matching phenomenon at the base of the wave mixing.

[0006] In a parametric amplifier performing four-wave mixing (by Kerr effect), two waves are incident: the pump wave with pulse wp and the wave to be amplified or signal wave with pulse eus. The amplifier transfers energy from the pump wave to the signal wave, which is therefore amplified, and also creates a complementary wave with a pulse wc to keep the energy unchanged.

[0007] Superconducting elements such as Josephson junctions are the material support in which the nonlinearity that forms the basis of parametric amplification of the waves passing through them occurs. This is known as a Josephson parametric amplifier (JPA). These JPA amplifiers are effective in the microwave range.

[0008] To achieve significant gains, standing wave amplifiers have been proposed, built around a resonant cavity, as in Planat, 2018, Phys. Rev. Applied 11, 034014 -2019. The bandwidth is of the order of 45 MHz. It can be multiplied by 10 by performing impedance matching.

[0009] Traveling wave parametric amplifiers (TWPAs) have also been proposed, for example US8878626B2. In these structures, many nonlinear elements connected in a chain form a transmission line for signal propagation. Phase matching can be achieved by the presence of resonators on the line, as in Macklin, Science, 2015, 350, 6258, 307, or by modulation of the line dimension, as in US8878626B2.

[0010] In US2018 / 0034425A1, the chain-connected elements are assemblies of Josephson junctions mounted in loops. The loops are coupled asymmetrically, and each by four poles. Regulation is achieved by adjusting the intensity of a magnetic flux that is arranged to pass through the loops.

[0011] Amplification in TWPAs is achieved through a wave mixing process resulting from the coupling between propagation modes in the nonlinear medium: the medium is excited with a strong pump wave, at frequency wp, causing the amplification of a weaker signal, at frequency eus, and the creation of a complementary wave, at frequency œc. The bandwidth of a TWPA can be a few GHz. In practice, a distortion in the dispersion relation is generated by opening a photon gap in the dispersion relation by periodically modulating the transmission line or by creating a band gap by introducing resonant elements into the transmission line. However, significant ripples are observed in the gain profile. And the amplification band is fixed by design.

[0012] Known traveling wave microwave amplifiers or TWPAs pass the signal from the amplifier input to the amplifier output but also the existing noise from the output to the input. They are therefore said to be reciprocal.

[0013] Such reciprocal traveling wave microwave amplifiers, due to their reciprocal nature, require use in conjunction with an additional microwave component called an isolator, which allows the isolation mentioned in the introduction to be achieved. This component, placed between the low-power microwave source to be amplified and the traveling wave amplifier (and therefore generally in a very low temperature enclosure), allows the filtering, in the direction from the playback devices and towards the source, of the parasitic signals generated by the traveling wave amplifier itself or by the components or the environment existing on the other side of the amplifier, such as an additional amplifier in HEMT (high electron mobility transistor) technology.But these microwave isolators have a large physical footprint (and use magnetic fields: they are components containing permanent magnets, whose magnetic fields can affect qubits and superconducting amplifiers) and cannot be integrated directly onto a chip. It is therefore difficult or uneconomical to place such an amplifier in a very low temperature enclosure, in which one also wishes to multiplex many signals. Alternatively or in conjunction with isolators, circulators have been used, but these components also have a large footprint.

[0014] Lecoq et al., Phys. Rev. Applied 7, 024028 2017 and Lecoq et al., Phys. Rev Lett. 126, 020502, 2020 discuss the use of a Josephson junction parametric amplifier with a loop in frequency space. These authors argue that this amplifier protects the readout cavity and the qubit on which they are implement. The system is a standing wave system requiring four microwave sources, and its bandwidth - about 10 MHz wide - is narrow.

[0015] Ranzani et al., Physs Rev. Applied 8, 054035, 2017, presented a transmission line based on Josephson junctions, in groups of five with a total of 740 junctions, inserted between 50 transmission line segments. A wp pump tone (or wave) modulates the line inductance and enables frequency conversion of a signal propagating together with the pump.

[0016] Frattini et al., Appl. Phys. Lett. 1 10, 222603, 2017, presented a dipole called SNAIL, a superconducting nonlinear asymmetric inductive element, consisting of four Josephson junctions distributed over two branches, including three large junctions (tunnel energy Ej) on one branch and one small junction (tunnel energy ccEj) on the other branch. This element allows three-wave mixing. Then Frattini et al. Phys. Rev. Applied 10, 054020, 2018 disclosed a chain of 20 SNAIL dipole elements (consisting of 3 large junctions Lj and one small junction Lj / oc) in series subjected to an identical magnetic flux for all elements, varied from 0 to 0.5 flux quantum. The authors discuss the optimization of amplification by three-wave mixing, and the minimization of four-wave mixing.

[0017] Perelshtein et al. 2022, Physical Review Applied 18, 024063 uses 1632 SNAILs comprising only three Josephson junctions: a small junction, aEJ, on one branch and two large junctions, EJ, on the other branch with the same dipole orientation over the entire chain. For zero flux quantum, the line impedance is less than 50 and there is no 3-wave mixing. At a flux quantum of 0.4, these authors observe some Probe mixing, and some 4-wave mixing.

[0018] Ranadive et al., Nature Communications, 2022, 13, 1737 proposed to place SNAILs in an inverted manner relative to each other with respect to the field, in an alternating manner, to suppress three-wave mixing processes (SNAILs are placed with alternating magnetic flux polarity, i.e., they are physically oriented so that the magnetic flux polarization between two adjacent SNAIL cells is reversed, taking advantage of the fact that the g3 nonlinearity factor of 2 ndorder quantifying the three-wave mixing phenomenon is an odd function of the external flux). The system comprises, at 20 mK, 700 cells spanning 6 mm, each cell containing a superconducting loop with three large Josephson junctions (critical current 10) and one small one (low critical current, rIO) in two arms. The ratio between the critical current of the small and large Josephson junctions (r) is chosen such that the amplitudes of the second-order nonlinearity (g3) and the third-order nonlinearity (g4) are anti-correlated. These authors found a significant amplification for a flux quantum of 0.5, with reference to the unit magnetic flux quantum <t>0. These authors thus present a broadband transmission line with a strong third-order nonlinearity - which therefore allows four-wave mixing - the factor g4 which can be adjusted to positive or negative values. The reported phenomenon is called reverse Kerr phase matching. The combined bandwidth is announced at 3 GHz, without gaps in the transmission. Summary of the invention

[0019] In addition to being reciprocal, TWPAs suffer from reflections at the junction with transmission lines, and from back-emission.

[0020] The present invention solves the problem of isolation, because the proposed principles break the reciprocity of existing amplifiers and therefore do not allow the propagation of signals or noise from the amplifier output to its input and therefore to the device under test.

[0021] For this purpose, a microwave signal amplifier is proposed comprising a chain of nonlinear inductive dipole elements each forming an asymmetric superconducting loop with Josephson junctions, said chain being arranged between an input of the chain for applying a signal to be amplified of known frequency and an output of the chain at which an output signal develops, the amplifier further comprising a controllable magnetic flux generation system for circulating a current in said loops, the amplifier further comprising a first microwave pump and a means for coupling said input of the chain to the first pump, the first pump generating through the first coupling means a wave in the chain in the direction from the input to the output of frequency adjusted to transfer power to the microwaves propagating in a band around the frequency of the signal to be amplified.

[0022] The amplifier further comprises a second microwave pump and a second means for coupling said output of the chain to said second pump, the second pump generating through the second coupling means a wave in the chain in the direction from the output to the input, at a frequency different from that of the first pump and so as to attenuate in said direction from the output to the input the microwaves propagating in a band (generally different from the previous band mentioned for amplification) around the frequency of the signal to be amplified. This attenuation can take place by a frequency conversion mechanism.

[0023] The principles thus stated make it possible to obtain a traveling wave parametric amplifier which is also a powerful isolator in the reverse direction, over a bandwidth of several hundred MHz (typically 800 MHz) and which can be adjusted over several GHz, with a center frequency of typically 6 GHz. With such a device, additional bulky and magnetic microwave isolators, or circulators, are avoided: it is possible to have a connection without an intermediate isolator between the microwave source to be amplified and the parametric amplifier. The footprint of the elements to be installed in the cryogenic enclosure is therefore controlled. Amplification can be obtained with a gain of 20 dB while obtaining an isolation of 30 dB in the other direction.

[0024] Remarkably, these principles require only two microwave pumps, not three or four like some prior art devices. This is remarkable from the perspective of scaling up.

[0025] With these principles, moreover, the gain profile is regular, without abrupt ripples as in devices in which phase matching is obtained by modulation of the line width based on simple Josephson junctions, which present impedance mismatches.

[0026] According to advantageous and optional features: - the dipole elements of the chain can be identical, and that the magnetic flux is, related to the quantum of flux of the loops, set to be non-zero modulo 0.5, and preferably between 0.05 and 0.35, and preferably between 0.1 and 0.3. - nonlinear asymmetric inductive elements of the chain may comprise between their two poles a first and a second branch connected in parallel to each other, the first branch consisting of a network of at least two Josephson junctions in series, the second branch consisting of a single Josephson junction or a second network of Josephson junctions in series, a number of Josephson junctions in the second network being less than a number of Josephson junctions in the first network; - the dipole elements and the magnetic flux generation system may be configured such that the asymmetric loops of successive dipole elements along the chain are subjected to a magnetic flux of similar intensity but whose direction is opposite from an asymmetric loop to a following loop in the chain, and preferably, from an asymmetric loop to the immediately following loop in the chain; - the nonlinear asymmetric inductive elements may comprise between their two poles a branch comprising one or more identical small Josephson junctions and a branch comprising one or more identical large Josephson junctions, a critical current ratio r between small junction and large junction being between 0.01 and 0.25, and preferably between 0.05 and 0.20. - superconducting nonlinear asymmetric inductive elements can comprise between their two poles a branch comprising a single Josephson junction called a small junction and a branch comprising three identical Josephson junctions called large junctions, in series. - the nonlinear asymmetric inductive elements may comprise small and large Josephson junctions, the small Josephson junctions having an inductance of between 1300 and 2500 pH, preferably between 1600 and 2200 pH, or the large Josephson junctions having an inductance of between 100 and 300 pH, preferably between 140 and 260 pH. - the magnetic flux generation system can consist of a single electromagnet developing a uniform magnetic field over the entire chain. - the chain can comprise between 500 and 1300 nonlinear inductive dipole elements, and preferably between 600 and 850. - the first pump can emit a microwave at a frequency between 5.2 and 10.5 GHz, preferably between 6.0 and 10 GHz. - the second pump can emit a microwave at a frequency between 8.4 and 13.5 GHz, preferably between 9.7 and 13.5 GHz. - a frequency difference between the microwaves emitted by the first pump and the second pump may be between 2 and 6 GHz, the second pump emitting at a higher or lower frequency than the first. - the signal to be amplified can be present at a frequency of the order of between 5.0 and 7.8 GHz, preferably between 6.0 and 6.4 GHz. Typically, it is a signal from a qubit. - the first coupling means may be a diplexer applying a high-pass filter to the microwaves of the first pump and directing them towards the chain, and applying a low-pass filter to the microwaves of the signal to be amplified and also directing them towards the chain. - the second coupling means may be a diplexer applying a high-pass filter to the microwaves from the second pump and directing them to the chain, and applying a low-pass filter to the microwaves from the chain and directing them to a reading chain. List of figures

[0027] Figures 1 and 2 show a circuit according to one embodiment of the invention.

[0028] Figure 3 is a graph of the numerical values ​​of the attenuation obtained.

[0029] Figure 4 is a view of the evolution of the gain values, as a function of the flux and the frequency.

[0030] Figure 5 is a view of the numerical gain values ​​in one direction and in the opposite direction. Detailed description

[0031] [Fig. 1] As shown in Fig. 1, a chain of superconducting asymmetric nonlinear inductive (SNAIL) elements is inserted in the center of a transmission line section, indicated in the figure as transmission line 50 - an impedance value used in a standard manner, for example coaxial, and advantageously differential between two conductive lines.

[0032] The device consists of several hundred dipole cells connected in series extending in total over a few millimeters in length, each cell containing a superconducting loop with three large Josephson junctions (high critical current I0 or inductance L) and one small one (low critical current rIO with r<1 or inductance L / a with a<1) in one arm and the other arm of the loop respectively.

[0033] The SNAIL chain—typically 700 SNAILs, but other values ​​are possible—is fabricated on a silicon substrate using evaporation and deposition techniques. It connects a conductive line upstream of the chain to a conductive line downstream. The second conductive lines upstream and downstream are connected directly by a conductor. A dielectric layer, such as alumina, placed between the SNAIL chain and the copper line provides the ground capacitance required to match the transmission line impedance to a standard 50 Ω environment.

[0034] Within each SNAIL the junctions are all coplanar and the SNAILs in the chain are all coplanar. A current-carrying coil a few centimeters in diameter is used to bias the device, with low field asymmetry across the chain of SNAIL loops.

[0035] In one embodiment, SNAILs are constructed with an alternation whereby, moving from one end of the chain to the other end of the chain, for every second SNAIL, the branch with large Josephson junctions is on the left and the one with small Josephson junctions is on the right, and then for the next SNAIL, the branch with large Josephson junctions is on the right and the one with small Josephson junctions is on the left. This has already been presented in Ranadive et al., Nature Communications, 2022, 13, 1737. The SNAILs are thus placed with alternating magnetic flux polarity, being physically oriented so as to reverse the magnetic flux polarization for two adjacent SNAIL cells. In another embodiment, the alternation is not done at each SNAIL, but every two SNAILs, or every N SNAILs, where N is an integer.

[0036] From the left of the figure to the right, the signal to be amplified with pulse eus (around 6 GHz, but without this being essential, other values ​​can be used) which is of low intensity, as well as a pump pulse of controlled intensity, significant in its intensity, with pulse œp not far from eus but for example higher than it, are introduced into the transmission line, which constitutes a wave mixing amplification chain.

[0037] By a wave mixing phenomenon, which is estimated, without wishing to be bound by this explanation, to be based mainly on a four-wave mixing - noted in figure 4WM for four wave mixing - the signal at the pulsation eus develops amplified by wave mixing at the end of the amplification chain, on the right of the figure. At this end is of course present the pump signal wp which has traveled through the chain. There is also at this end one or more complementary waves or idlers, not shown because they are not amplified.

[0038] From the right of the figure to the left, the eus pulse signal that has reached the end of the chain or beyond and has been amplified is very partially reflected in the transmission line due to any change in impedance, however modest. Noise in the frequency range of the eus signal may also be present and travel along the amplification line, from the output and in the direction of the source of the signal to be amplified.

[0039] A pump tone, of controlled intensity, significant in power, of pulsation wp', for example a little further from eus than wp (therefore wp' > wp) is introduced into the chain by the output, wp' depends on the method of manufacturing the Josephson junctions.

[0040] By a phenomenon of wave mixing, which is estimated, without wishing to be bound by this explanation, to be based mainly on a three-wave mixing - noted in figure 3WM for three wave mixing - the signal at the eus pulse and the noise at this frequency and at neighboring frequencies are attenuated when they travel, in the opposite direction to the direction intended for amplification, the amplification chain, from the output to the input.

[0041] At this input end, of course, the pump signal wp' that has traveled down the chain since the output is present, as well as a frequency-shifted wave ws+p', of much higher frequency. They are both outside frequencies likely to disturb the source of the signal to be amplified (typically a qubit), because they are far removed from ws.

[0042] [Fig. 2] As shown in Figure 2, the emissions of the object to be tested DUT (device under test) 10 and a pump microwave source 20 are, in a 20 mK cryostat chamber, directed respectively towards the two channels of a diplexer 30, the pump being processed by a high-pass filter in one of the channels, and the signal of the object to be tested by a low-pass filter in the other channel. The two waves are directed by the diplexer 30 via its common port then serving as an output towards the parametric amplifier 40 according to the invention also in the 20 mK cryostat chamber, and the signal to be amplified emerges as explained in connection with Figure 1. It is directed to the common gate of a diplexer 50, which is connected by its channel gates to respectively a microwave source 60, and an isolator 70 followed by a low noise amplifier LNA 80 located in a higher temperature stage, for example 4 K, which gives the amplified signal to a reading chain 90.The waves from the microwave source 60 are filtered by a high-pass filter before being transmitted to the output of the parametric amplifier 40. The waves leaving the parametric amplifier 40 are processed by a low-pass filter before being transferred to the isolator 70. The LNA amplifier 80 produces noise which propagates in the transmission line in the direction of the diplexer 50 but is blocked by the isolator 70. Conversely, no isolator is present on the transmission line between the object to be tested DUT 10 and the parametric amplifier 40, nor between the parametric amplifier 40 and the diplexer 50. This is a considerable advantage, when one knows the size and the disadvantages of the presence of such an isolator in a cryostat chamber, typically close to a qubit or another device to be tested.The diplexer 30 optionally filters by the low-pass filter that it interfaces between the parametric amplifier 40 and the object to be tested DUT 10 the pump tone wp' which has traveled through the chain from the output, as well as the frequency-shifted wave ws+p'.

[0043] [Fig. 3] Figure 3 shows the isolation obtained in the opposite direction to amplification, with the system according to the invention. The microwave source 60 provides a pump tone at 10.2 GHz, and this creates a 1 GHz wide isolation band and 20 dB of attenuation gain, which is remarkable.

[0044] [Fig. 4] Figure 4 shows the system gain in one direction or the other, for a pump tone frequency of 10.17 GHz, as a function of the flux applied to the parametric amplifier, on the abscissa and as a function of the frequency to be amplified or attenuated, on the ordinate. The darker the shade, the more the signal is attenuated, the lighter the shade, the more it is amplified. We observe a periodicity along the abscissa axis, with a period of one flux quantum of the loops of the parametric amplifier. We also observe symmetries with respect to the abscissas 0 flux quantum, 0.5 flux quantum and 1 flux quantum. Attenuation zones are very visible from 0 to 0.5 flux quantum and from 0.5 flux quantum to 1 flux quantum, moving in frequency as a function of the flux value, width in frequency and flux decreasing until becoming zero as we approach 0 and 0.5 flux quantum, values ​​where this attenuation is no longer observed.Thus, as soon as the flux quantum value deviates from 0 and 0.5 flux quantum, it is possible to implement attenuation.

[0045] [Fig. 5] Figure 5 shows the implementation of an embodiment of the invention, with a pump tone for 9 GHz amplification and a pump tone for 12 GHz isolation. For a bandwidth of 250 MHz, an isolation of 20 dB in the direction to be isolated and a gain of 20 dB in the direction to be amplified is obtained.

[0046] Regarding the construction of SNAILs, if we denote by n1 the number of Josephson junctions on one arm (the small junctions), and n2 the number of Josephson junctions on the other arm (the large junctions), then we prefer that n1 be different from n2 (n1 + n2). In particular, if there is a single small junction, at least two large Josephson junctions are required. We can choose large junctions at 200 pH and small junctions at 1500 pH.

[0047] The ratio of critical currents between junctions in each arm (small and large junctions), as well as the number of junctions in each arm are parameters to adjust the presence of attenuation triggered by a pump of a given frequency, and amplification triggered by a pump of another frequency.< / t>

Claims

CLAIMS 1. A microwave signal amplifier comprising a chain (40) of nonlinear inductive dipole elements each forming an asymmetric superconducting Josephson junction loop, said chain being arranged between an input of the chain for applying a signal to be amplified of known frequency (10) and an output of the chain at which an output signal develops, the amplifier further comprising a controllable magnetic flux generation system for circulating a current in said loops, the amplifier further comprising a first microwave pump (20) and a first coupling means (30), the first coupling means coupling said input of the chain to the first pump (20),the first pump (20) generating through the first coupling means (30) a wave in the chain (40) in the direction from input to output and of frequency adjusted to transfer power to microwaves propagating in a band around the frequency of the signal to be amplified, the amplifier being further characterized in that it further comprises a second microwave pump (60) and a second coupling means (50), the second coupling means (50) coupling said output of the chain to said second pump (60), the second pump (60) generating through the second coupling means (50) a wave in the chain (40) in the direction from output to input, at a frequency different from that of the first pump (20) and so as to attenuate in said direction from output to input microwaves also propagating in a band around the frequency of the signal to be amplified., 2. Microwave signal amplifier according to claim 1, characterized in that the dipole elements of the chain are identical, and that the magnetic flux is, relative to the quantum of flux of the loops, adjusted to be non-zero modulo 0.5, and preferably between 0.05 and 0.35, and preferably between 0.1 and 0.

3.

3. Microwave signal amplifier according to claim 1 or claim 2, characterized in that nonlinear asymmetrical inductive elements of the chain comprise between their two poles a first and a second branch connected in parallel to each other, the first branch consisting of a network of at least two Josephson junctions in series, the second branch consisting of a single Josephson junction or a second network of Josephson junctions in series, a number of Josephson junctions in the second network being less than a number of Josephson junctions in the first network.

4. Microwave signal amplifier according to one of claims 1 to 3, characterized in that the dipole elements and the magnetic flux generation system are configured in such a way that the asymmetric loops of the successive dipole elements along the chain are subjected to a magnetic flux of similar intensity but whose direction is opposite from an asymmetric loop to a following loop in the chain, and preferably, from an asymmetric loop to the immediately following loop in the chain.

5. Microwave signal amplifier according to one of claims 1 to 4, characterized in that the nonlinear asymmetrical inductive elements comprise between their two poles a branch comprising one or more identical small Josephson junctions and a branch comprising one or more identical large Josephson junctions, a critical current ratio r between small junction and large junction being between 0.01 and 0.25, and preferably between 0.05 and 0.

20.

6. Microwave signal amplifier according to one of claims 1 to 5, characterized in that the superconducting nonlinear asymmetric inductive elements comprise between their two poles a branch comprising a single Josephson junction called a small junction and a branch comprising three identical Josephson junctions called large junctions, in series.

7. Microwave signal amplifier according to one of claims 1 to 6, characterized in that the nonlinear asymmetrical inductive elements comprise small and large Josephson junctions, the small Josephson junctions having an inductance of between 1300 and 2500 pH, preferably between 1600 and 2200 pH or the large Josephson junctions having an inductance of between 100 and 300 pH, preferably between 140 and 260 pH.

8. Microwave signal amplifier according to one of claims 1 to 7, characterized in that the magnetic flux generation system consists of a single electromagnet developing a uniform magnetic field over the entire chain.

9. Microwave signal amplifier according to one of claims 1 to 8, characterized in that the chain comprises between 500 and 1300 nonlinear inductive dipole elements, and preferably between 600 and 850.

10. Microwave signal amplifier according to one of claims 1 to 9, characterized in that the first pump emits a microwave at a frequency between 5.2 and 10.5 GHz, preferably between 6.0 and 10 GHz.

11. Microwave signal amplifier according to one of claims 1 to 10, characterized in that the second pump emits a microwave at a frequency between 8.4 and 13.5 GHz, preferably between 9.7 and 13.5 GHz.

12. Microwave signal amplifier according to one of claims 1 to 11, characterized in that a frequency difference between the microwaves emitted by the first pump and the second pump is between 2 and 6 GHz, the second pump emitting at a higher frequency than the first.

13. Microwave signal amplifier according to one of claims 1 to 12, characterized in that the signal to be amplified is present at a frequency of the order of between 5.0 and 7.8 GHz, preferably between 6.0 and 6.4 GHz.

14. Microwave signal amplifier according to one of claims 1 to 13, characterized in that the first coupling means is a diplexer applying a high-pass filter to the microwaves of the first pump and directing them towards the chain, and applying a low-pass filter to the microwaves of the signal to be amplified and also directing them towards the chain.

15. Microwave signal amplifier according to one of claims 1 to 14, characterized in that the second coupling means is a diplexer applying a high-pass filter to the microwaves from the second pump and directing them towards the chain, and applying a low-pass filter to the microwaves coming from the chain and directing them towards a reading chain.

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