RU177295U1 - FLACKSON RING DETECTOR - Google Patents

Abstract

The utility model relates to cryogenic electronics and can be used in measurement technology, radio engineering and information systems (including quantum) to measure weak magnetic fluxes (less than 0.1 quantum of magnetic flux) with a relatively weak inverse effect on the object of study. More specifically, a flaxon ring detector is proposed that includes two DC sources for the operating point setting system, two phaxon generators, two microwave radiation detection systems, two Josephson transmit lines in the form of ring contacts connected by a superconducting jumper magnetically coupled to the object under study. The utility model provides the ability to determine both the absolute value and the direction of the effective magnetic moment of the investigated quantum system and additionally reduces the inverse effect of the detector on the object of research, which is especially important for use in quantum information processing devices. 6 c.p. f-ly, 5 ill.

Description

The utility model relates to cryogenic electronics and can be used in measurement technology, radio engineering and information systems (including quantum) to measure weak magnetic fluxes (less than 0.1 quantum of magnetic flux) with a relatively weak inverse effect on the object of study.

To detect weak magnetic fields, devices based on superconducting quantum interferometers (SQUID, from the English SQUID - Superconducting Quantum Interference Device) are actively used, which have high sensitivity and low noise temperature, as well as are compatible with other superconducting devices in the signal reception and processing complex. Such a SQUID is a superconducting ring containing one or two Josephson junctions, and the phase incursion of the superconducting order parameter along the contour is associated with the total magnetic flux through the ring. Depending on the intended applications, SQUID includes various matching and measuring devices.

The development of modern technologies has set the task of creating detectors based on SQUID structures that can capture magnetic fields from nanoscale objects (for example, superconducting flux qubits) and large molecules.

From the analysis of the prior art, a method is known for reading the state of fluxed quantum bits - artificial mesoscopic atoms, for which the characteristic transition frequencies between stationary states lie in the gigahertz range - using a two-contact superconducting quantum interferometer and magnetic flux conversion system [patent application WO 2012064974 A2, publ. 05/18/2012].

From the analysis of the prior art there is also known a device for measuring the characteristics of a magnetic field (nano-magnetometer) based on SQUID with two superconducting rings [patent US 7863892 B2, publ. January 4, 2011], which provides an increase in sensitivity when working with objects of research of small sizes.

Also described is a method of creating SQUID with a characteristic size of key elements of the order of 100 nm [patent application US 20100097056 A1, publ. 04/22/2010].

The disadvantages of the above systems are their strong inverse effect on the object of study and the inability to implement “fast” and non-destructive measurements of the states of quantum objects.

The principles of matching the input and output circuits of an SQUID-based amplifier-converter with a load have been studied in detail for a range of up to 0.1 GHz [JP patent 61115536 A, publ. 06/03/1986].

In the document [JPH patent 01245605 A, publ. 09/29/1989] describes an amplifier-converter of a magnetic signal in direct current SQUID, in which a second SQUID is used as an adjustable inductive element of the matching circuit to electrically adjust the coordination of the interferometer with a cooled preamplifier.

In another device on a low-temperature (operating temperature 4.2 K) SQUID, the magnetoresistive amplification principle is implemented, which provides the measurement of low currents, voltages, or magnetic fields without feedback and noise reduction systems, but the description does not indicate the possibility of using the measured frequencies and amplitudes in the range of interest signals [patent DE 4003060 A1, publ. 08/08/1991].

However, both the operating frequency range and the linearity of the conversion of the magnetic signal into voltage (which is extremely necessary in situations where it is necessary to isolate the weak signal of interest to us against the background of strong “noise”) for devices based on a single low-temperature SQUID are insufficient for modern high-frequency applications. Also, the existing level of energy dissipation and reverse influence on the object under study during operation makes it impossible to use such devices in reading systems in quantum information processing devices.

In the prior art [patent US 7095227 B2, publ. 08/22/2006] also described an amplifier on a sequential chain of SQUIDs that allows you to use a DC source as a power source and occupying a small area. Such amplifiers can be used, for example, in sensitive systems for paramagnetic resonance imaging [patent US 8179135 B2, publ. 05/15/2012], and also as an input unit of superconducting analog-to-digital converters [patent US 7928875 B2, publ. 04/19/2011].

However, such an amplifier device allows only a relatively small linear gain of the signal to be achieved.

To increase the linearity of the volt-stream conversion of systems based on SQUIDs in the document [patent US 7453263 B2, publ. November 18, 2008] a special feedback scheme was proposed that contains an additional Josephson contact, however, the proposed method for improving the amplifier based on SQUID significantly limits the maximum operating frequency and, accordingly, spoils the time resolution for a detector using this principle.

You can also use SQUID as a tunable element of the oscillatory circuit of a parametric amplifier [patent application JP 2009225213 A, publ. 10/01/2009].

However, the characteristic operating frequency of such an amplifier will be determined by the parameters of the oscillatory circuit, i.e. will be noticeably less than 1 GHz. It is also necessary to note such a drawback as the impossibility of implementing, on the basis of such a principle, "short-range" minimally disturbing measurements of the magnetic moment of quantum systems, which are of serious practical interest today.

From the analysis of the prior art, proposals are also known for the use of driver amplifiers for the gigahertz range (up to tens of GHz) based on chains of SQUIDs, divided into pairs isolated from the earth, to reduce stray capacitances in the system [patent US 6486756 B2, publ. 11/26/2002].

However, such amplifiers are only suitable for digital applications and cannot be used to amplify an analog signal.

Also useful for further discussion is the signal amplifier of fast single-quantum (BOC) logic, converting them at the output into voltage pulses of sufficient magnitude for use by semiconductor electronics, the operation of which is based on a technical solution [US patent 6917216, publ. 04/11/2003], working on the separation and re-reflection of the output BOC-pulse to obtain sufficient values of the output voltage pulses.

However, this proposal is again designed exclusively for use in digital devices and requires ultra-weak signal pairing with a high-quality analog “receiving device” for use in detectors.

In the document [patent application WO 2012123642, publ. September 20, 2012] a low-noise amplifier with a sensitivity close to the quantum limit is described. The principle of operation of this amplifier is based on the use of a single Josephson contact, shunted due to the reactive impedance connected in parallel with it.

The disadvantage of this approach is the weak gain, low linearity, low saturation temperature of the resulting amplifier, which is also extremely difficult to make quite miniature.

Attention should be paid to publications devoted to the presentation of theoretical approaches to the description of the principles of operation of Josephson ballistic detectors, which are also applicable in quantum information processing systems. In particular, an experimental measurement of the rotation of approximately 1000 electron spins using SQUID with a superconducting loop size of less than 1 μm has been described [Jamet M. et al. Magnetic Anisotropy of a Single Cobalt Nanocluster / Physical Review Letters, 2001, V. 86, N. 20, pp. 4676-4679].

The scheme of a ballistic detector proposed in the works of a number of authors [Averin D. V. et al. Rapid ballistic readout for flux qubits / Physical Review B, 2006, V. 73, pp. 094504-1 ÷ 094504-12; Herr A. et al. Design of a ballistic fluxon qubit readout / Superconductor Science and Technology, 2007, V. 20, pp. S450-S454], similar to an optical interferometer, one arm of which weakly interacts with the measured object (for example, a quantum system). The “shoulders” of the interferometer are two Josephson transmission lines (DPL), which are distributed Josephson junctions, each of which propagates a soliton-like wave of currents and voltages (phaxon). Interaction with the measured object leads to the acceleration or deceleration of the vial in one of the DPL. Thus, information about the state of the quantum system is translated into a time delay between the outputs of the phials from the DPL of the detector, which is then read.

The disadvantage of such a ballistic detector circuit from the point of view of maximizing the signal-to-noise ratio is the use of an additional reference line, which leads to an increase in the internal noise of the detector. The disadvantages include the opposite effect of the poles of the current dipole on the flaxon. This reciprocal effect leads to a significant decrease in the signal. As a modification of the scheme, one can propose an effective splitting of the dipole into monopoles, for the implementation of which the DPL is carried out from the generator of single-quantum pulses to the middle of the dipole and branches into two branches, each of which continues towards one of the monopoles. In this case, the initial single-quantum pulse generates two pulses at the branch point, one in each branch. Pulses formed synchronously each interact with one of the monopoles, accelerating or decelerating in accordance with its direction, after which the mutual time delay is detected in the comparison circuit.

In the experiments [Fedorov K.G. et al. Josephson vortex coupled to a flux qubit / Applied Physics Letters, 2013, V. 102, pp. 132602-1 ÷ 132602-4; Fedorov KG. et al. Fluxon Readout of a Superconducting Qubit / Physical Review Letters, 2014, V. 112, pp. 160502-1 ÷ 160502-5] used a single annular DPL and measured the deviation of the cyclic frequency of rotation of the vial.

The disadvantages of this approach include the lack of dependence of the deviation of the detector frequency from the sign of the measured field (polarity of the induced current dipole), which makes it impossible to distinguish the quantum states of the object under study.

The claimed invention is devoid of this drawback and allows for the measurement of super-weak signals due to the influence of a magnetic field from the object of study on the dynamics of phaxons simultaneously in two Josephson ring DPLs.

The technical result of the present invention lies in the possibility of determining both the absolute value and direction of the effective magnetic moment of the investigated quantum system. An additional technical result is to reduce the inverse effect of the detector on the object of research, which is especially important for use in quantum information processing devices.

The indicated technical result is achieved by a flaxon ring detector, which includes two direct current sources for the operating point setting system, two flaxon generators, two microwave radiation detection systems, two Josephson transmit lines in the form of ring contacts, connected by a superconducting jumper magnetically connected to the object under study.

The device is a superconducting quantum interferometer, in which ring DPLs are used instead of concentrated Josephson junctions. In each ring, the phaxons are symmetrically defined, and to minimize the inverse effect, the phaxons rotate in opposite directions. The response to an ultra-weak magnetic field from the object of research will be the deviation of the rotation frequency of the fluxons (the same in both rings - the frequency is equalized due to the superconducting coupling of the rings) from the original and the phase shift of the oscillations.

In one of the preferred embodiments, the detector is characterized in that the Josephson transmission lines are each made in the form of a ring-forming thin-film structure, comprising: a lower superconducting electrode deposited on a substrate, an insulator layer deposited on a lower superconducting electrode, an upper superconducting electrode with current leads, deposited on an insulator layer .

In one of the preferred embodiments, the detector is characterized in that the Josephson transmission line is each made in the form of a loop closed in a ring of layered thin-film structures connected by superconducting connecting lines, the thin-film structure comprising a lower superconducting electrode deposited on a substrate, an insulator layer, and an upper superconducting electrode with current leads.

The detector can also be characterized by the fact that niobium, aluminum or an alloy based on these metals are used as the material of the superconducting jumper, the lower and upper superconducting electrodes, and superconducting connecting lines.

The detector can also be characterized in that alumina Al ₂ O _{3 is} used as the material of the insulator layer.

The detector may also be characterized in that the thickness of the lower superconducting electrode and the upper superconducting electrode is 50-500 nm.

In addition, the proposed detector can also be characterized by the fact that the thickness of the insulator layer is 1-20 nm.

The invention is illustrated by the following drawings.

In FIG. 1 is a schematic diagram of a detector based on one ring Josephson transmission line (top view).

In FIG. 2 is a schematic diagram of a detector based on two Josephson annular transmission lines (top view) connected to an object of research proposed symmetrically through a superconducting jumper; there is also presented a cross-sectional diagram of parts of long (larger than the Josephson magnetic field penetration length λ _j ) Josephson junctions used as a DPS, where S is a superconductor, I is an insulator, black arrows indicate the direction of the current flow induced by the magnetic field of the object under study, red arrows - directions of distribution of phaxons.

; длина каждой ДПЛ равна L=10 λ_J.In FIG. Figure 3 shows the calculated deviation of the rotational speed of the phaxons in the detector DPL as a response to an ultra-weak magnetic field for the current range of the operating point setting j / j _c = 0.02 ... 0.5; dimensionless damping parameter of ring contacts α = 0.2; dimensionless inductance of the receiving loop

; the length of each DPL is L = 10 λ _J.

; безразмерного параметра демпфирования кольцевых контактов а=0.2; длина каждой ДПЛ равна L=7λ_J.In FIG. Figure 4 shows the amplitude of the frequency response of the detector when the applied magnetic flux changes from zero to half a quantum for the range of the supply current j / j _c = 0.02 ... 0.5 and the range of normalized inductance

; dimensionless damping parameter of ring contacts a = 0.2; the length of each DPL is L = 7λ _J.

.In FIG. 5 shows the calculated deviation of the rotational speed of the phaxons for the range of the length of annular DPLs L / λ _j = 2 ... 10; dimensionless damping parameter of ring contacts a = 0.2; current for setting the operating point j / j _c = 0.2 and dimensionless inductance of the receiving loop

.

The positions in the drawings (figures) indicate: 1 - current sources for the system of setting the operating point and generation of phials; 2 and 3 - Josephson transmission lines; 4 - object of study; 5 - superconducting jumper; 6 - a region of space in which fields realizing magnetic coupling are localized between the object of study and the superconducting jumper of the detector; 7 — microwave radiation detection systems; 8 — lower superconducting electrode; 9 - insulator layer; 10 - upper superconducting electrode.

Implementation of a utility model.

The detector (see Fig. 1 and Fig. 2) contains two Josephson transmission lines (2 and 3), which form two closed paths along which they rotate at a certain frequency determined by the system for setting the operating point (1), Josephson vortices (flaxons), thus generating microwave electromagnetic radiation, for the detection of which the device of the microwave radiation detection system (7) is used.

The scattering of each of the phaxons on the current dipole induced by the magnetic field of the object of study (4) creates a measurable frequency shift of the detected radiation. The measured frequency shift provides information on the state of the object of study. These measurements can be made practically non-destructive of the state of a quantum system acting as an object of research if the frequency of measurements is matched with the natural frequency of the object of research (if the detector is used in quantum information processing systems). The idea of the claimed symmetrization of the circuit is that both phaxons are scattered by current inhomogeneities, and each phaxon is scattered at only one pole of the dipole. This can be achieved by attaching a communication loop to both Josephson lines of the detector, as shown in FIG. 2.

The difference between such a detector and ordinary SQUID is the absence of resistive shunts for the Josephson contacts used, and at the same time, there is no undesirable hysteresis on the current-voltage characteristic of the device as a whole; studies of the state of a quantum object are conveniently carried out by measuring the frequency of microwave radiation; there are optima of the detector sensitivity as a function of the operating point reference current shown in FIG. 3.

In FIG. Figure 3 shows the frequency response Δω / ω _p from the magnetic flux Ф / Ф ₀ entering the detector, the magnitude of which is normalized to the magnitude of the quantum; Δω = ω-ω ₀ , where ω ₀ is the rotation frequency at a zero signal Ф = 0. The value of the damping parameter α = 0.2 is typical of Josephson junctions made for ballistic detectors.

In FIG. 4 demonstrates how to increase the inductance of the response magnitude falls: magnitude response is defined as Δω _max = ω (when F = F _0/2) -ω (when F = 0). The ring length for this calculation was chosen slightly less than in the previous case in accordance with the optimization carried out with respect to this parameter and presented in FIG. 5. It is seen that the optimum length approximately coincides with the size of the fluxon. The current for setting the operating point was chosen in the vicinity of the optimum j / j _c = 0.2, where the response form is noticeably different from the usual one for SQUID. It can be seen that with a decrease in the length of the ring, the form approaches it. The phase shift of the oscillations of the phaxons in the circular DPL will be proportional to the flow applied to the detector and can also be used to obtain information about the state of the object of study

The above sources confirm the validity and relevance of the approach to the implementation of superconducting detectors. Technological applicability: for the implementation of the inventive device, materials used in cryoelectronic technology and known to specialists can be used. As a substrate, on which all the elements of the detector are located, any standard substrates (silicon, sapphire, etc.) can be used. As a material for the insulator layer - aluminum oxide. As a material for superconducting electrodes, niobium, niobium nitride, vanadium, indium, tin, lead. Typical layer thicknesses for the patented topology are in the range technologically feasible for thin-film electronics. As a generator of single-quantum pulses, devices of fast single-quantum logic can be used [K. Likharev K. et al. RSFQ logic / memory family: a new Josephson-junction technology for sub-terahertz-clock-frequency digital systems // IEEE Transactions on Applied Superconductivity, 1991, V. 50, N. 1, pp. 3-28], well known from the prior art and allowing to generate phaxons with the necessary reliability. Also, modern cryogenic electromagnetic radiation detectors make it possible to fix with the necessary accuracy the frequency of the wave generated during the circular motion of the phaxons along the Josephson transmission line [Terai N. et al. Low-jitter single flux quantum signal readout from superconducting single photon detector / Optics express, 2012, V. 20, N. 18, pp. 20115-20123].

Claims (7)

1. A flaxon ring detector, which includes two DC sources for the operating point setting system, two flaxon generators, two microwave radiation detection systems, two Josephson transmission lines in the form of ring contacts connected by a superconducting jumper magnetically connected to the object under study. 2. The detector according to claim 1, characterized in that the Josephson transmission lines are each made in the form of a ring-forming thin-film structure, comprising: a lower superconducting electrode deposited on a substrate, an insulator layer deposited on a lower superconducting electrode, an upper superconducting electrode with current leads, deposited on insulator layer. 3. The detector according to claim 1, characterized in that the Josephson transmission line is each made in the form of a loop closed in a ring of layered thin-film structures connected by superconducting connecting lines, while the thin-film structure contains a lower superconducting electrode deposited on a substrate, an insulator layer, an upper superconducting electrode with current leads. 4. The detector according to claim 2 or 3, characterized in that the material of the superconducting jumper, the lower and upper superconducting electrodes, superconducting connecting lines used niobium, aluminum or an alloy based on these metals. 5. The detector according to claim 2 or 3, characterized in that the aluminum oxide Al ₂ O _{3 is} used as the material of the insulator layer. 6. The detector according to claim 2 or 3, characterized in that the thickness of the lower superconducting electrode and the upper superconducting electrode is 50-500 nm. 7. The detector according to claim 2 or 3, characterized in that the thickness of the insulator layer is 1-20 nm.

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