Quantum sensing with tunable superconducting qubits: optimization and speed-up

Sensing and metrology play an important role in fundamental science and applications by fulfilling the ever-present need for more precise data sets and by allowing researchers to make more reliable conclusions on the validity of theoretical models. Sensors are ubiquitous. They are used in applications across a diverse range of fields including gravity imaging, geology, navigation, security, timekeeping, spectroscopy, chemistry, magnetometry, healthcare, and medicine. Current progress in quantum technologies has inevitably triggered the exploration of the use of quantum systems as sensors with new and improved capabilities. This article describes the optimization of the quantum-enhanced sensing of external magnetic fluxes with a Kitaev phase estimation algorithm based on a sensor with tunable transmon qubits. It provides the optimal flux biasing point for sensors with different maximal qubit transition frequencies. An estimation of decoherence rates is made for a given design. The use of $2-$ and $3-$qubit entangled states for sensing are compared in simulation with the single qubit case. The flux sensing accuracy reaches $10^{-8}\cdot\Phi_0$ and scales with time as $\sim\ 1/t$ which proves the speed-up of sensing with high ultimate accuracy.Comment: 13 pages, 7 figures, 1 table. arXiv admin note: substantial text overlap with arXiv:2103.1102

Scalable cryoelectronics for superconducting qubit control and readout

Quantum computing promises an exponentially higher computational power than classical computers; although all the building blocks have become available, certain constraints still prevent quantum advantage. The fundamental challenge in building a practical quantum computer is integrating thousands of highly coherent qubits with the control and readout electronics. The need for a high-coherence qubit drives the effort for quantum error correction algorithms to create fault-tolerant quantum systems. Error correction becomes tangible in a quantum processor only in large numbers of qubits. Thus, the other challenge is reducing the number of physical interconnects (coaxial lines) between the quantum–classical interface and bulky room-temperature electronics. To interface thousands of qubits, interconnects can be reduced by bringing the control and readout electronics near the quantum processor. Cryogenic complementary metal–oxide–semiconductor (CMOS) technology has been an ideal candidate for this purpose. Integrated control and readout at cryogenic temperatures require low power dissipation circuit designs and techniques such as frequency-division multiplexing (FDM) due to the finite cooling power of a dilution refrigerator. Herein, an overview of each building block in a superconducting quantum computer is provided, focusing on scalability. Furthermore, this article is concluded with an outlook discussing current challenges and future directions for the scalable superconducting control and readout

Coherent superconducting qubits from a subtractive junction fabrication process

Josephson tunnel junctions are the centerpiece of almost any superconducting electronic circuit, including qubits. Typically, the junctions for qubits are fabricated using shadow evaporation techniques to reduce dielectric loss contributions from the superconducting film interfaces. In recent years, however, sub-micron scale overlap junctions have started to attract attention. Compared to shadow mask techniques, neither an angle dependent deposition nor free-standing bridges or overlaps are needed, which are significant limitations for wafer-scale processing. This comes at the cost of breaking the vacuum during fabrication, but simplifies integration in multi-layered circuits, implementation of vastly different junction sizes, and enables fabrication on a larger scale in an industrially-standardized process. In this work, we demonstrate the feasibility of a subtractive process for fabrication of overlap junctions. In an array of test contacts, we find low aging of the average normal state resistance of only 1.6\% over 6 months. We evaluate the coherence properties of the junctions by employing them in superconducting transmon qubits. In time domain experiments, we find that both, the qubit life- and coherence time of our best device, are on average greater than 20\,\si{\micro\second}. Finally, we discuss potential improvements to our technique. This work paves the way towards a more standardized process flow with advanced materials and growth processes, and constitutes an important step for large scale fabrication of superconducting quantum circuits.Comment: 8 pages, 7 figure

Characterizing Niobium Nitride Superconducting Microwave Coplanar Waveguide Resonator Array for Circuit Quantum Electrodynamics in Extreme Conditions

The high critical magnetic field and relatively high critical temperature of niobium nitride (NbN) make it a promising material candidate for applications in superconducting quantum technology. However, NbN-based devices and circuits are sensitive to decoherence sources such as two-level system (TLS) defects. Here, we numerically and experimentally investigate NbN superconducting microwave coplanar waveguide resonator arrays, with a 100 nm thickness, capacitively coupled to a common coplanar waveguide on a silicon chip. We observe that the resonators' internal quality factor (Qi) decreases from Qi ~ 1.07*10^6 in a high power regime ( = 27000) to Qi ~ 1.36 *10^5 in single photon regime at temperature T = 100 mK. Data from this study is consistent with the TLS theory, which describes the TLS interactions in resonator substrates and interfaces. Moreover, we study the temperature dependence internal quality factor and frequency tuning of the coplanar waveguide resonators to characterise the quasiparticle density of NbN. We observe that the increase in kinetic inductance at higher temperatures is the main reason for the frequency shift. Finally, we measure the resonators' resonance frequency and internal quality factor at single photon regime in response to in-plane magnetic fields B||. We verify that Qi stays well above 10^4 up to B|| = 240 mT in the photon number = 1.8 at T = 100 mK. Our results may pave the way for realising robust microwave superconducting circuits for circuit quantum electrodynamics (cQED) at high magnetic fields necessary for fault-tolerant quantum computing, and ultrasensitive quantum sensing

Engineering the microwave to infrared noise photon flux for superconducting quantum systems

Electromagnetic filtering is essential for the coherent control, operation and readout of superconducting quantum circuits at milliKelvin temperatures. The suppression of spurious modes around transition frequencies of a few GHz is well understood and mainly achieved by on-chip and package considerations. Noise photons of higher frequencies – beyond the pair-breaking energies – cause decoherence and require spectral engineering before reaching the packaged quantum chip. The external wires that pass into the refrigerator and go down to the quantum circuit provide a direct path for these photons. This article contains quantitative analysis and experimental data for the noise photon flux through coaxial, filtered wiring. The attenuation of the coaxial cable at room temperature and the noise photon flux estimates for typical wiring configurations are provided. Compact cryogenic microwave low-pass filters with CR-110 and Esorb-230 absorptive dielectric fillings are presented along with experimental data at room and cryogenic temperatures up to 70 GHz. Filter cut-off frequencies between 1 to 10 GHz are set by the filter length, and the roll-off is material dependent. The relative dielectric permittivity and magnetic permeability for the Esorb-230 material in the pair-breaking frequency range of 75 to 110 GHz are measured, and the filter properties in this frequency range are calculated. The estimated dramatic suppression of the noise photon flux due to the filter proves its usefulness for experiments with superconducting quantum systems

Strong magnon-photon coupling with chip-integrated YIG in the zero-temperature limit

The cross-integration of spin-wave and superconducting technologies is a promising method for creating novel hybrid devices for future information processing technologies to store, manipulate, or convert data in both classical and quantum regimes. Hybrid magnon-polariton systems have been widely studied using bulk Yttrium Iron Garnet (Y$_{3}$Fe$_{5}$O$_{12}$, YIG) and three-dimensional microwave photon cavities. However, limitations in YIG growth have thus far prevented its incorporation into CMOS compatible technology such as high quality factor superconducting quantum technology. To overcome this impediment, we have used Plasma Focused Ion Beam (PFIB) technology -- taking advantage of precision placement down to the micron-scale -- to integrate YIG with superconducting microwave devices. Ferromagnetic resonance has been measured at millikelvin temperatures on PFIB-processed YIG samples using planar microwave circuits. Furthermore, we demonstrate strong coupling between superconducting resonator and YIG ferromagnetic resonance modes by maintaining reasonably low loss while reducing the system down to the micron scale. This achievement of strong coupling on-chip is a crucial step toward fabrication of functional hybrid quantum devices that advantage from spin-wave and superconducting components.Comment: 10 pages, 6 figure

Experiments with a transmon artificial atom - state manipulation and detection of magnetic fields

The field of quantum computation and simulation has its origins in the early 1980s, when the limitations of the existing paradigm of classical computing machines became apparent. The continuous miniaturization of circuit elements and the increase in their number per unit area will ultimately lead to practical difficulties and to the manifestation of quantum phenomena. This foresight triggered the research work for the invention of new principles of computation. The physical laws of our world are fundamentally quantum mechanical; that is why quantum systems have started to be considered as platforms for possible more powerful computing systems and simulators. Superconducting quantum circuits offer one of the most convenient and promising architectures in this field of research. They are macroscopic and, as a result, provide a better controllability. At the same time they can be produced with customary electronics fabrication methods and they are easily integrable with nowadays electronics.  This dissertation contains experimental studies of fully coplanar superconducting quantum circuits comprising a transmon type artificial atom coupled to a quarter-wavelength waveguide resonator. This circuit represents the simplest simulator of light-matter interaction and acts as a testbed for the gate operations needed to control the quantum state in the field of quantum computation. The stimulated Raman adiabatic passage and the shortcut to its adiabaticity were experimentally studied as methods for the efficient population transfer between the ground and the second excited state of the transmon. The possibility of using a hybrid adiabatic-nonadiabatic pulse sequences for preparing an arbitrary quantum three-level state was shown theoretically. The operation of gates based on geometric phases was implemented on the same type of superconducting structure. Finally, the structure was used as a magnetic flux sensor. The magnetic flux resolution of this sensor is enhanced by the use of two properly modified phase estimation algorithms and it is potentially limited only by the Heisenberg uncertainty principle. The superiority of the realized sensor over the standard classical measurement done on the same sample is clearly demonstrated. This experiment indicates the utility of superconducting quantum circuits for the tasks of quantum metrology

Agroecological role of biohumus on sod-podzolic soil during irrigation of the rump-timothy grass mixture

It has been established that it is possible to increase the productivity of grasslands on sod-podzolic soil with the introduction of biohumus against the background of irrigation. The optimal variant of the experiment with the introduction of vermicompost at the rate of 8 t/ha. The research results revealed an increase in the content of basic nutrients in the soil by 0.2 … 4 mg/100 g of soil, activation of the cellulose-degrading activity of the soil twice, which was characterized as strong on the Zvyagintsev scale. The content of organic matter in the soil increased to 0.28 t/ha. The plant density increased by 1.5 times, the height – 2 times, the yield of the grass mixture increased on average to almost 5 t/ha, the quality of products improved, which corresponded to the zootechnical norm in almost all parameters. The cost of production amounted to 2.04 rubles/kg, conditionally net income – 3.64 rubles. In the summer of 2019, the research results passed the first year of approbation at Igor VyacheslavovichBelousov LLC on an area of 1.5 hectares. The yield was 4.8 t/ha of dry matter, which is 31% higher than the control option – traditional technology

Analysis of commodity traffic in the European macro-region

One of the key industries of any state is the transport industry. It plays a significant role in the development of the country’s economy and ensuring its defense capability. Therefore, the development of the transport industry is always relevant for Russia with its vastness and climatic conditions. In this work, at the first stage, the country’s cargo turnover by mode of transport is considered and the current state of the transport system, in particular, water transport, is analyzed. At the second stage, the concept of multimodal transportation is considered and the possibility of using multi-agent systems for automating management processes in water transport is being studied