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| 2. |
- Mahashabde, Sumedh, 1985, et al.
(författare)
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A Frequency Selective Surface based focal plane receiver for the OLIMPO balloon-borne telescope
- 2015
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 5:1, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a Frequency Selective Surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident sub-mm radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window and with variable temperature black body source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of Noise Equivalent power (NEP) is also presented.
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| 3. |
- Osman, Amr, 1993, et al.
(författare)
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Simplified Josephson-junction fabrication process for reproducibly high-performance superconducting qubits
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:6
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a simplified fabrication technique for Josephson junctions and demonstrate superconducting Xmon qubits with T1 relaxation times averaging above 50 μs (Q > 1.5 × 1 0 6). Current shadow-evaporation techniques for aluminum-based Josephson junctions require a separate lithography step to deposit a patch that makes a galvanic, superconducting connection between the junction electrodes and the circuit wiring layer. The patch connection eliminates parasitic junctions, which otherwise contribute significantly to dielectric loss. In our patch-integrated cross-type junction technique, we use one lithography step and one vacuum cycle to evaporate both the junction electrodes and the patch. This eliminates a key bottleneck in manufacturing superconducting qubits by reducing the fabrication time and cost. In a study of more than 3600 junctions, we show an average resistance variation of 3.7% on a wafer that contains forty 0.5 × 0.5-cm2 chips, with junction areas ranging between 0.01 and 0.16 μm2. The average on-chip spread in resistance is 2.7%, with 20 chips varying between 1.4% and 2%. For the junction sizes used for transmon qubits, we deduce a wafer-level transition-frequency variation of 1.7%-2.5%. We show that 60%-70% of this variation is attributed to junction-area fluctuations, while the rest is caused by tunnel-junction inhomogeneity. Such high frequency predictability is a requirement for scaling-up the number of qubits in a quantum computer.
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| 4. |
- Scigliuzzo, Marco, 1987, et al.
(författare)
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Controlling Atom-Photon Bound States in an Array of Josephson-Junction Resonators
- 2022
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Ingår i: Physical Review X. - 2160-3308. ; 12:3
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Tidskriftsartikel (refereegranskat)abstract
- Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light -matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here, we report on the concept and implementation of a novel microwave architecture consisting of an array of compact superconducting resonators in which we have embedded two frequency -tunable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single-and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tunable-range interactions and photon transport experiments in the nonlinear regime.
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| 5. |
- Scigliuzzo, Marco, 1987, et al.
(författare)
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Extensible quantum simulation architecture based on atom-photon bound states in an array of high-impedance resonators
- 2021
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light-matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here we report on the concept and implementation of a novel microwave architecture consisting of an array of compact, high-impedance superconducting resonators forming a 1 GHz-wide pass band, in which we have embedded two frequency-tuneable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single- and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tuneable-range interactions and photon transport experiments in nonlinear regime
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| 6. |
- Scigliuzzo, Marco, 1987, et al.
(författare)
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Primary Thermometry of Propagating Microwaves in the Quantum Regime
- 2020
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Ingår i: Physical Review X. - 2160-3308. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- The ability to control and measure the temperature of propagating microwave modes down to very low temperatures is indispensable for quantum information processing and may open opportunities for studies of heat transport at the nanoscale, also in the quantum regime. Here, we propose and experimentally demonstrate primary thermometry of propagating microwaves using a transmon-type superconducting circuit. Our device operates continuously, with a sensitivity down to 4×10-4 photons/Hz and a bandwidth of 40 MHz. We measure the thermal occupation of the modes of a highly attenuated coaxial cable in a range of 0.001 to 0.4 thermal photons, corresponding to a temperature range from 35 mK to 210 mK at a frequency around 5 GHz. To increase the radiation temperature in a controlled fashion, we either inject calibrated, wideband digital noise, or heat the device and its environment. This thermometry scheme can find applications in benchmarking and characterization of cryogenic microwave setups, temperature measurements in hybrid quantum systems, and quantum thermodynamics.
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| 7. |
- Bengtsson, Andreas, 1991-
(författare)
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Carbon fibres from lignin-cellulose precursors
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector. The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs. This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view. The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties. A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (<2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route.
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| 8. |
- Bengtsson, Andreas, 1991
(författare)
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Degenerate and nondegenerate Josephson parametric oscillators for quantum information applications
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Parametric oscillations are well studied phenomena, with applications in amplification, quantum optics, and quantum information processing. They can occur as a parameter of a system, such as the resonant frequency, is being modulated or “pumped” by an external field. A nonlinearity of the system can then transfer power from the pumping frequency to two frequencies called signal and idler. When the signal falls within a resonance, and when the pump amplitude exceeds an instability threshold, parametric oscillations occur. When signal and idler fall within the same resonance, the pumping is called degenerate.Due to somewhat different implementations, in combination with rich nonlinear physics, the details of the parametric oscillations can differ in different systems. In this work, we expand on the research done on parametric oscillations using a superconducting microwave resonator with a tunable boundary condition. Previously, a degenerate Josephson parametric oscillator (JPO) has been demonstrated by modulation of this boundary condition at twice the resonator's resonant frequency. We further use the JPO to implement a novel read-out method for a superconducting qubit. Moreover, we demonstrate a different, nondegenerate regime of the JPO, which we denote the NJPO, by modulating the frequency at the sum of two resonant frequencies of a multimode resonator.Both the JPO qubit read-out and the NJPO have applications within quantum information processing. The perhaps most promising platform for quantum information processing is represented by the circuit-QED architecture with superconducting resonators and artificial atoms, where the two lowest atomic levels represent the qubit. We make these circuits using lithographic techniques, and control and measure them at low temperature using microwaves. The qubit's state is fragile and difficult to read out with high fidelity. To this end, we have developed a method based on the JPO, in which the qubit state is mapped onto a zero-amplitude or a large-amplitude state of the JPO. We achieved a large contrast (185±15 photons), therefore eliminating the need for a following quantum-limited parametric amplifier. Our readout fidelity was 81.5 %, and by carefully modeling we can distinguish fidelity loss from the qubit and the readout, respectively. This analysis displays an actual readout fidelity of 98.7 %.An alternative model for quantum computing is based on continuous variables, and uses harmonic oscillators instead of qubits. Entangled states, which can be used as quantum resources, can then be created, for example, by two-mode squeezing of the oscillator ground state. The state of the NJPO produces correlated oscillations in its two modes, which might be useful for continuous-variable quantum computing. In this work we fully characterize the classical properties of the NJPO, and show good quantitative agreement with a theoretical model.
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| 9. |
- Bengtsson, Andreas, 1991, et al.
(författare)
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Improved Success Probability with Greater Circuit Depth for the Quantum Approximate Optimization Algorithm
- 2020
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Ingår i: Physical Review Applied. - 2331-7019. ; 14:3
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Tidskriftsartikel (refereegranskat)abstract
- Present-day, noisy, small or intermediate-scale quantum processors-although far from fault tolerant-support the execution of heuristic quantum algorithms, which might enable a quantum advantage, for example, when applied to combinatorial optimization problems. On small-scale quantum processors, validations of such algorithms serve as important technology demonstrators. We implement the quantum approximate optimization algorithm on our hardware platform, consisting of two superconducting transmon qubits and one parametrically modulated coupler. We solve small instances of the NP (nondeterministic polynomial time)-complete exact-cover problem, with 96.6% success probability, by iterating the algorithm up to level two.
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| 10. |
- Bengtsson, Andreas, 1991, et al.
(författare)
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Nondegenerate parametric oscillations in a tunable superconducting resonator
- 2018
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:14
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Tidskriftsartikel (refereegranskat)abstract
- We investigate nondegenerate parametric oscillations in a superconducting microwave multimode resonator that is terminated by a superconducting quantum interference device (SQUID). The parametric effect is achieved by modulating magnetic flux through the SQUID at a frequency close to the sum of two resonator-mode frequencies. For modulation amplitudes exceeding an instability threshold, self-sustained oscillations are observed in both modes. The amplitudes of these oscillations s how good quantitative agreement with a theoretical model. The oscillation phases are found to be correlated and exhibit strong fluctuations which broaden the oscillation spectral linewidths. These linewidths are significantly reduced by applying a weak on-resonant tone, which also suppresses the phase fluctuations. When the weak tone is detuned, we observe synchronization of the oscillation frequency with the frequency of the input. For the detuned input, we also observe an emergence of three idlers in the output. This observation is in agreement with theory indicating four-mode amplification and squeezing of a coherent input.
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