| 1. |
- Burnett, J., et al.
(författare)
-
PC2: Identifying noise processes in superconducting resonators
- 2013
-
Ingår i: 2013 IEEE 14th InternationalSuperconductive Electronics Conference, ISEC 2013. - 9781467363716 ; , s. Art. no. 6604284-
-
Konferensbidrag (refereegranskat)abstract
- Extensive studies of dielectric loss due to two level fluctuators (TLFs) in superconducting resonators have provided routes for low loss resonators. The research is motivated not only by the use of resonators as detectors and in quantum information processing, but more generally due to TLFs being a source of noise and decoherence in all quantum devices. In this work a frequency locked loop was used to measure frequency fluctuations at timescales in excess of 104 seconds, thereby accurately probing the TLF induced low- frequency noise of the resonator. Our measurement method lead to very high statistical confidence even for very long timescales, and here we can therefore present results explicitly identifying power dependent flicker frequency noise (S = 1/fa where a=1) persisting down to the mHz level.
|
|
| 2. |
- de Graaf, Sebastian Erik, 1986, et al.
(författare)
-
Charge Qubit Coupled to an Intense Microwave Electromagnetic Field in a Superconducting Nb Device: Evidence for Photon-Assisted Quasiparticle Tunneling
- 2013
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 111:13, s. Art. no. 137002-
-
Tidskriftsartikel (refereegranskat)abstract
- We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stückelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stückelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.
|
|
| 3. |
- de Graaf, Sebastian Erik, 1986, et al.
(författare)
-
Direct Identification of Dilute Surface Spins on Al2 O3: Origin of Flux Noise in Quantum Circuits
- 2017
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 118:5, s. 057703-
-
Tidskriftsartikel (refereegranskat)abstract
- An on-chip electron spin resonance technique is applied to reveal the nature and origin of surface spins on Al2O3. We measure a spin density of 2.2×1017 spins/m2, attributed to physisorbed atomic hydrogen and S=1/2 electron spin states on the surface. This is direct evidence for the nature of spins responsible for flux noise in quantum circuits, which has been an issue of interest for several decades. Our findings open up a new approach to the identification and controlled reduction of paramagnetic sources of noise and decoherence in superconducting quantum devices.
|
|
| 4. |
- de Graaf, Sebastian Erik, 1986, et al.
(författare)
-
Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evid ence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.
|
|
| 5. |
- Geaney, S., et al.
(författare)
-
Near-Field Scanning Microwave Microscopy in the Single Photon Regime
- 2019
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- The microwave properties of nano-scale structures are important in a wide variety of applications in quantum technology. Here we describe a low-power cryogenic near-field scanning microwave microscope (NSMM) which maintains nano-scale dielectric contrast down to the single microwave photon regime, up to 109 times lower power than in typical NSMMs. We discuss the remaining challenges towards developing nano-scale NSMM for quantum coherent interaction with two-level systems as an enabling tool for the development of quantum technologies in the microwave regime.
|
|
| 6. |
- Keyser, Ailsa K.V., et al.
(författare)
-
Pulsed electron spin resonance of an organic microcrystal by dispersive readout
- 2020
-
Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 321
-
Tidskriftsartikel (refereegranskat)abstract
- We establish a testbed system for the development of high-sensitivity Electron Spin Resonance (ESR) techniques for small samples at cryogenic temperatures. Our system consists of a NbN thin-film planar superconducting microresonator designed to have a concentrated mode volume to couple to a small amount of paramagnetic material, and to be resilient to magnetic fields of up to 400mT. At 65mK we measure high-cooperativity coupling (C≈19) to an organic radical microcrystal containing 1012 spins in a pico-litre volume. We detect the spin–lattice decoherence rate via the dispersive frequency shift of the resonator. Techniques such as these could be suitable for applications in quantum information as well as for pulsed ESR interrogation of very few spins to provide insights into the surface chemistry of, for example, the material defects in superconducting quantum processors.
|
|
| 7. |
- Leppäkangas, Juha, 1979, et al.
(författare)
-
Effects of quasiparticle tunnelling in a circuit-QED realization of a strongly driven two-level system
- 2013
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 1361-6455 .- 0953-4075. ; 46:22, s. Art. no. 224019-
-
Tidskriftsartikel (refereegranskat)abstract
- We experimentally and theoretically study the frequency shift of a driven cavity coupled to a superconducting charge qubit. In addition to previous studies, here we also consider drive strengths large enough to energetically allow for quasiparticle creation. Quasiparticle tunnelling leads to the inclusion of more than two charge states in the dynamics. To explain the observed effects, we develop a master equation for the microwave dressed charge states, including quasiparticle tunnelling. A bimodal behaviour of the frequency shift as a function of gate voltage can be used for sensitive charge detection. However, at weak drives, the charge sensitivity is significantly reduced by nonequilibrium quasiparticles, which induce transitions to a non-sensitive state. Unexpectedly, at high-enough drives, the quasiparticle tunnelling enables a very fast relaxation channel to the sensitive state. In this regime, the charge sensitivity is thus robust against externally injected quasiparticles and the desired dynamics prevail over a broad range of temperatures. We find very good agreement between the theory and experiment over a wide range of drive strengths and temperatures.
|
|
| 8. |
- Ranjan, V., et al.
(författare)
-
Spin-Echo Silencing Using a Current-Biased Frequency-Tunable Resonator
- 2022
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 129:18
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to control microwave emission from a spin ensemble is a requirement of several quantum memory protocols. Here, we demonstrate such ability by using a resonator whose frequency can be rapidly tuned with a bias current. We store excitations in an ensemble of rare-earth ions and suppress on demand the echo emission ("echo silencing") by two methods: (1) detuning the resonator during the spin rephasing, and (2) subjecting spins to magnetic field gradients generated by the bias current itself. We also show that spin coherence is preserved during silencing.
|
|
