Superconducting kinetic inductance detectors for astrophysics

Vardulakis, Α. I. G.; Withington, S.; Goldie, D. J.; Glowacka, D.

doi:10.1088/0957-0233/19/1/015509

Cited by 32 publications

(34 citation statements)

References 18 publications

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“…The only difference was in a single measurement on a Nb resonator, when two discontinuities where seen when sweeping the frequency in the same direction. 42 This observation can now be understood in terms of an inadvertent double-dip on the power absorption curve of the resonant circuit, leading to three stable and two unstable quasiparticle temperature states.…”

Section: Discussionmentioning

confidence: 98%

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Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

Visser

Withington

Goldie

2010

Journal of Applied Physics

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A model is presented for readout-power heating in kinetic inductance detectors. It is shown that the power dissipated by the readout signal can cause the temperature of the quasiparticle system in the superconducting resonator to switch between well-defined states. At low readout powers, only a single solution to the heat balance equation exists, and the resonance curve merely distorts as the readout power is increased. At high readout powers, three states exist, two of which are stable, and the resonance curve shows hysteretic switching. The power threshold for switching depends on the geometry and material used but is typically around Ϫ70 dBm for Aluminum resonators. A comprehensive set of simulations is reported, and a detailed account of the switching process is given. Experimental results are also shown, which are in strong qualitative agreement with the simulations. The general features of the model are independent of the precise cooling function, and are even applicable for resonators on suspended, thermally isolated, dielectric membranes, where an increase in quasiparticle lifetime is expected. We discuss various extensions to the technique, including the possibility of recovering the cooling function from large-signal measurements of the resonance curve.

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Section: Discussionmentioning

confidence: 98%

“…A detailed experimental study is needed before this question can be answered but it is interesting to note that Nb resonators show, experimentally, the same general behavior as our simulations predict. 42 …”

Section: B Niobium and Tantalummentioning

confidence: 99%

Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

Visser

Withington

Goldie

2010

Journal of Applied Physics

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“…[1][2][3][4][5][6][7] Such resonators are also being used in quantum computing experiments [8][9][10] and for sensing nanomechanical motion. 11 We previously reported that excess frequency noise is universally observed in these resonators and suggested that two-level systems ͑TLSs͒ in dielectric materials 14,15 may be responsible for this noise.…”

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confidence: 99%

Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators

Gao

Daal

Day

et al. 2008

Applied Physics Letters

324

318

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We present measurements of the temperature-dependent frequency shift of five niobium superconducting coplanar waveguide microresonators with center strip widths ranging from 3 to 50 m, taken at temperatures in the range of 100-800 mK, far below the 9.2 K transition temperature of niobium. These data agree well with the two-level system ͑TLS͒ theory. Fits to this theory provide information on the number of TLSs that interact with each resonator geometry. The geometrical scaling indicates a surface distribution of TLSs and the data are consistent with a TLS surface layer thickness of the order of a few nanometers, as might be expected for a native oxide layer. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2906373͔Superconducting microresonators have attracted substantial interest for low temperature detector applications due to the possibility of large-scale microwave frequency multiplexing.1-7 Such resonators are also being used in quantum computing experiments [8][9][10] and for sensing nanomechanical motion. 11 We previously reported that excess frequency noise is universally observed in these resonators and suggested that two-level systems ͑TLSs͒ in dielectric materials 14,15 may be responsible for this noise.12 TLS effects are also observed in superconducting qubits.9 The TLS hypothesis is strongly supported by the observed temperature dependence of the noise and also by the observation of temperature-dependent resonance frequency shifts that closely agree with the TLS theory. 13 To make further progress, it is essential to constrain the location of the TLSs, to determine whether they exist in the bulk substrate or in surface layers, perhaps oxides on the exposed metal or substrate surfaces, or in the interface layers between the metal films and the substrate. In this paper, we provide direct experimental evidence for a surface distribution of TLSs.TLSs are abundant in amorphous materials 14,15 and have electric dipole moments that couple to the electric field E ជ of our resonators. For microwave frequencies and at temperatures T between 100 mK and 1 K, the resonant interaction dominates over relaxation, which leads to a temperaturedependent variation of the dielectric constant given bywhere is the frequency, ⌿ is the complex digamma function, and ␦ = Pd 2 / 3⑀ represents the TLS-induced dielectric loss tangent at T = 0 for weak nonsaturating fields. Here, P and d are the two-level density of states and dipole moment, as introduced by Phillips. 16 Equation ͑1͒ has been extensively used to derive values of Pd 2 in amorphous materials. If TLSs are present in superconducting microresonators, their contribution to the dielectric constant described by Eq. ͑1͒ could be observable as a temperature-dependent shift in the resonance frequency. Indeed, it has recently been suggested that the small anomalous low-temperature frequency shifts often observed in superconducting microresonators may be due to TLS effects, 17,18 and, in fact, excellent fits to the TLS theory can be obtained. 13 Assuming that the TLSs ar...

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“…The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system ͑TLS͒ model for amorphous dielectrics. Superconducting microresonators are useful for photon detection, [1][2][3][4][5][6][7] coupling to qubits, [8][9][10] superconducting quantum interference device multiplexers, 11,12 and studying basic physics. [13][14][15][16] Such resonators have excess noise 2,17 that is equivalent to a jitter of the resonance frequency, likely caused by two-level tunneling systems ͑TLSs͒ in amorphous dielectrics.…”

mentioning

confidence: 99%

Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators

Kumar

Gao

Žmuidzinas

et al. 2008

Applied Physics Letters

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We present measurements of the temperature and power dependence of the resonance frequency and frequency noise of superconducting niobium thin-film coplanar waveguide resonators carried out at temperatures well below the superconducting transition ͑T c = 9.2 K͒. The noise decreases by nearly two orders of magnitude as the temperature is increased from 120 to 1200 mK, while the variation of the resonance frequency with temperature over this range agrees well with the standard two-level system ͑TLS͒ model for amorphous dielectrics. These results support the hypothesis that TLSs are responsible for the noise in superconducting microresonators and have important implications for resonator applications such as qubits and photon detectors. 23 have highlighted TLS effects in superconducting microcircuits. While the TLS energy splitting ⌬E has a broad distribution, 22 a resonator with frequency f r is most sensitive to TLS with ⌬E ϳ hf r . The level populations and relaxation rates of such TLS vary strongly at temperatures T ϳ hf r / 2k B , or around 100 mK for the device studied here. Furthermore, such near-resonant TLS may saturate 18 for strong resonator excitation power P w . Hence, measurements of the power and temperature variation of the resonator frequency and noise, as presented in this letter, provide a strong test of the TLS hypothesis.We studied coplanar waveguide ͑CPW͒ quarterwavelength resonators 2,18 fabricated on a high-resistivity ͑ ജ 10 k⍀ cm͒ crystalline silicon substrate by patterning a 200 nm thick niobium film using a photoresist mask and a SF 6 inductively coupled plasma etch. In this device, TLS may be present in the native oxide surface layers on the metal film or substrate. 18 The resonator is capacitively coupled to a CPW feedline ͑Fig. 1͒ that has a 10 m wide center strip and 6 m gaps between the center strip and the ground plane. For the resonator, these dimensions are 5 and 1 m, respectively. The resonator length is 5.8 mm, corresponding to f r = 4.35 GHz. The coupling strength is set lithographically 17,18 ͑see Fig. 1͒ and is characterized by the coupling-limited quality factor Q c =5ϫ 10 5 . The device was cooled using a dilution refrigerator, and its temperature was measured to Ϯ5 mK accuracy using a calibrated RuO 2 thermometer mounted on the copper sample enclosure. The microwave readout ͑Fig. 1͒ uses a standard IQ homodyne mixing technique. 2,17 The IQ mixer's complex output voltage ͑f͒ = I͑f͒ + jQ͑f͒ follows a circular trajectory in the complex plane as the microwave excitation frequency f is varied, 18 and f r and Q r are determined by complex leastsquares fitting of this trajectory to a ten-parameter model:Here ␦x = ͑f − f r ͒ / f r is the fractional frequency offset, S 21 ͑r͒ is the complex forward transmission on resonance, B 0 + B 1 ␦x allows for a linear gain variation, 0 + 1 ␦x allows a similar linear phase variation, and B 2 and 2 specify the output offset voltages of the IQ mixer. The combined noise of the resonator and readout electronics is measured by tuning the synthesi...

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Superconducting kinetic inductance detectors for astrophysics

Cited by 32 publications

References 18 publications

Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

Readout-power heating and hysteretic switching between thermal quasiparticle states in kinetic inductance detectors

Experimental evidence for a surface distribution of two-level systems in superconducting lithographed microwave resonators

Temperature dependence of the frequency and noise of superconducting coplanar waveguide resonators

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