Search for Dark Photon Dark Matter with a Mass around 36.1 μeV Using a Frequency-tunable Cavity Controlled through a Coupled Superconducting Qubit

Abstract

We report the results of a search for dark photon dark matter using a cavity that employs a transmon qubit as a frequency tuner. The tuning mechanism utilizes the energy level shift arising from the mode mixing between the qubit and the cavity mode. This method is advantageous as it avoids the frictional heating and electromagnetic leakage associated with mechanical tuning. We searched for a dark matter signal in the mass range $36.132 - 36.179$ $μ$eV and found no significant evidence. As a result, we set the exclusion limit on the kinetic mixing parameter down to approximately $5 \times 10^{-13}$, surpassing the existing limit set by cosmology.

Figures (5)

• Figure 1: The experimental setup for the superconducting qubit and cavity. (a) Optical microscope image of the qubit used in this experiment. The scale of the large rectangle capacitance pads is $250µ m\times400µ m$. (b) The magnification of (a) capturing the SQUID loop in the qubit. (c) Photo of the copper cavity and the qubit in this experiment. The dimension of the cavity is $7mm \times 13mm \times 38mm$. The qubit is on a bridge of sapphire and in the center of the cavity. The cavity is surrounded by a NbTi superconducting coil to impose magnetic flux. (d) Photo of the cavity being loaded onto the 10mK stage of the dilution refrigerator. The refrigerator is located at the cryogenic research center, the University of Tokyo. To protect against the ambient magnetic flux, the sample is encapsulated by a mu-metal based magnetic shield.
• Figure 2: Schematic of the receiver chain used in this experiment. For the measurement, a spectrum analyzer (Keysight CXA N9000B) and a vector network analyzer (Keysight E5063A) were used. For the DC current modulation, Yokogawa GS200 was used as DC supply. The spectrum was amplified first by a HEMT and subsequently a series of room temperature amplifiers to detect weak signal. The switches at room temperature were used to switch between the transmission and reflection measurement and spectrum analyzer measurement and VNA measurement respectively. For the system noise calibration, a hotload was placed at the 10mK stage connected to the same RF circuit as the measured cavity.
• Figure 3: Relationship between the bias current flowing through the coil ($x$-axis) and the cavity frequency ($y$-axis). The color scale indicates the cavity transmittance, with the yellow region corresponding to the center of the cavity resonance as the function of the bias current. The red dashed line is the prediction by the Jaynes-Cummings model. The region marked by the black dashed lines and arrow corresponds to the approximate data range used in this study.
• Figure 4: The combined power excesses (blue dots) and standard deviations included statistical and systematic uncertainties (orange region).
• Figure 5: (Large box) Comparison with existing experimental limits and cosmological constraints, following caputoDarkPhotonLimits2021ariasWISPyColdDark2012. Existing results are indicated by gray shaded regions, while our result is shown as the orange line. We apply the random polarization, $\braket<\cos^2\theta>=1/3$. This plot was generated from caputoDarkPhotonLimits2021. (Small box) The detailed view of the exclusion limit of this experiment. Orange region is in the random polarization case, and the blue region case is in the worst case caputoDarkPhotonLimits2021.