Higher-order modes boost amplification capabilities of quantum detectors
Higher-order modes boost amplification capabilities of quantum detectors lead image
To detect faint signals from the decay of a subatomic particle — or from the magnetic fields of living organisms — devices typically use amplifiers to boost the signal. Superconducting quantum interference devices (SQUIDs) are widely used to amplify low-level electromagnetic signals with the advantages of low noise, high gain, and low power dissipation. In Applied Physics Letters (APL), researchers now report achieving significantly enhanced gain for SQUIDs at higher frequencies.
Basic SQUIDs are limited to frequencies of 100 MHz or below, but the microstrip SQUID amplifier (MSA) works from a few hundred megahertz to typically one gigahertz. The MSA was invented in 1998 to detect photons produced by the decay of axions, hypothetical elementary particles that could be the origin of cold dark matter. With the MSA, an integrated input coil is operated on top of the SQUID washer as a microstrip resonator. However, gain decreases with increasing frequency.
Instead of the usual microstrip length of one-half wavelength (λ/2), the new MSA operates at 3λ/2 or 5λ/2 with the winding sense for each λ/2 section reversed. With this configuration, the magnetic flux adds instead of canceling, resulting in a higher gain.
Co-authors Mück and Schmidt tested multiple versions of the new and improved MSA, measuring the gain as a function of signal frequency. On resonance, they found substantial improvements in gain. For instance, at 2.6 GHz the amplifier achieved a gain of 24 dB using a higher-order mode, as opposed to 10 dB less for an otherwise identical conventional MSA. “Their device worked like a bandit,” said co-author Clarke.
The modified device has significant implications not only for axion detection, but also potentially for reading out superconducting quantum bits in quantum computing.
Source: “Microstrip superconducting quantum interference device amplifier: Operation in higher-order modes,” by Michael Mück, Bernd Schmidt, and John Clarke, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.4985384 .
