Figure 1

(Color online) (a) Cartoon schematic of the QCD concept. Incident submillimeter radiation is coupled by an antenna into a superconducting absorber, generating quasiparticles. The quasiparticle density in the absorber is then measured with an SCB. (b) Circuit diagram of the SCB and its readout.Reuse & Permissions

Figure 2

(Color online) (a) Example of two-rate telegraph noise in the capacitance signal, recorded at the SCB degeneracy point. Data adapted from Ref. 14. (b) Phase-shift histogram, taken at the degeneracy point, showing two clearly separated peaks corresponding to odd and even-parity states. Note the large $\left(140°\right)$ phase shift between the two. The phase-shift signal in the QCD is an average taken over the entire time signal. (c) Phase-shift histograms as a function of gate voltage. The $z$ axis is plotted logarithmically to emphasize the presence of the minority (odd) parity state. White lines are theoretically predicted capacitance traces for the odd and even-parity states.Reuse & Permissions

Figure 3

(Color online) Schematic block diagram of proposed QCD readout electronics. Inset, lower right: Single pixel—A rf carrier signal excites the tank circuit of a particular detector pixel, producing a reflected signal that is phase shifted according the average charge state of the SCB. An ac bias voltage is applied, with an amplitude of $e/C_g$, which modulates the phase-shift signal by sweeping the SCB through one full gate period. A mixer demodulates the reflected rf signal at the bias voltage modulation frequency and a down-converter translates the result to dc. Main: Multiplexed readout—A low-frequency comb function (0–200 MHz) containing several frequency components is produced digitally and block up-converted, resulting in a comb of rf carrier frequencies, each corresponding to a particular detector. All of the SCB gate lines are tied together and modulated at the same frequency.Reuse & Permissions

Figure 4

(Color online) Measured aggregate phase noise in a test device oscillator with an input power of $-125\text{dBm}$. This device was fabricated using lower-$T_C$ Al/Ti/Au trilayer leads to suppress quasiparticle tunneling. The estimated phase noise includes contributions from oscillator phase noise, SCB charge noise, and noise in the amplifiers and electronics. Blue (jagged) curve is a periodogram of time-domain phase noise measured using an oscilloscope. Black (straight) line is a fit to a $1/f$ curve with a prefactor of $6.5°$ at 1 Hz.Reuse & Permissions

Figure 5

(Color online) Theoretical average phase response of the SCB readout oscillator as a function of detector loading power. Solid (blue) curve: Response with small absorber, $\Omega =0.1\mu {\text{m}}^3$, optimized for maximum sensitivity. Dashed (red) curve: Response with larger absorber, $\Omega =10\mu {\text{m}}^3$, optimized for higher saturation power or shorter wavelength radiation.Reuse & Permissions

Figure 6

(Color online) Noise-equivalent power as a function of signal modulation frequency for a variety of physical noise mechanisms, as described in the text. Simulations are performed with fixed temperature $T=100\text{mK}$ and incident power $P_s={10}^{-19}\text{W}$. Solid (black) line: mean-square sum of the NEP due to each noise mechanism. Dashed (blue) line: NEP due to telegraph noise. Dotted (green) line: NEP due to aggregate excess phase noise. Dash-dotted (red) line: NEP due to Fano noise. Solid horizontal (gold) line: NEP due to generation-recombination noise.Reuse & Permissions

Figure 7

(Color online) Noise-equivalent power as a function of operating temperature for a variety of physical noise mechanisms, as described in the text. Simulations are performed with fixed measurement time ${\tau }_m=10\text{ms}$ and incident power $P_s={10}^{-19}\text{W}$. The color scheme and line styles are identical to those of Fig. 6.Reuse & Permissions

Figure 8

(Color online) Noise-equivalent power as a function of loading power, as described in the text. Simulations are performed with fixed modulation time ${\tau }_m=10\text{ms}$ and operating temperature $T=100\text{mK}$. Solid (blue) line: mean-square total NEP due to all noise mechanisms. Dashed (green) line: Photon shot noise at a wavelength $\lambda =30\mu \text{m}$. Dotted (red) line: Photon shot noise at $\lambda =1\text{mm}$.Reuse & Permissions

Figure 9

(Color online) Saturation power as a function of frequency, for the sample parameters used in Fig. 8. Solid (blue) curve: Physical saturation power of the detector, as defined in the text. Dashed (green) curve: Critical power at which the detector ceases to be shot noise limited, as defined in the text, for $\lambda =30\mu \text{m}$. Dotted (red) curve: Shot noise limit for $\lambda =1\text{mm}$. The points where the shot noise limits drop rapidly off scale indicate frequency ranges where the detector is not shot noise limited at all.Reuse & Permissions

Figure 10

(Color online) Noise-equivalent power as a function of absorber volume $\Omega$ for fixed measurement time ${\tau }_m=10\text{ms}$, operating temperature $T=100\text{mK}$, and incident power $P_s={10}^{-19}\text{W}$. The color scheme and line styles are identical to those of Figs. 6, 7. While the sensitivity of the detector improves with a smaller absorber, engineering tradeoffs must be made with saturation power, and practicality of fabrication.Reuse & Permissions

Figure 11

(Color online) Comparison of QCD detector sensitivity as a function of wavelength with the detector requirements for the BLISS spectrometer. Detector requirements and spectrometer loading data are adapted from Ref. 15.Reuse & Permissions