Back to the Basic: Spin Maser for Quantum Information Technologies


OIST, Yuimaru Kubo

Current quantum information technologies at microwave frequencies require ultra-low temperature operations, typically at 10 – 100 millikelvin, because of the tiny energy of microwave photons.  One of the key technologies is an ultra-low noise amplification of microwave signals at millikelvin environments.  This has only been realized by superconducting Josephson parametric amplifiers (JPA), which are based on superconducting circuits.  However, JPAs have suffered from a smaller saturation power. The state-of-the-art JPA has a maximum input power of about -100 dBm (0.1 picowatts).  Moreover, JPAs do not properly work under strong magnetic fields due to the superconductivity. 

One of the other principles for amplifying microwave signals is maser, an acronym of “microwave amplification by stimulated emission of radiation”, with spins in crystals.  Although maser has been intensively studied in the late 1950s and early 1960s, it has been then forgotten behind because of the rise and progress of the semiconductor technologies. 

We demonstrate that this “maser amplifier” is indeed very interesting and promising for microwave quantum information and technology applications at millikelvin temperatures, where nobody has demonstrated spin maser operation.  Using P1 centers in diamond, we demonstrated a spin-based cavity amplifier with a gain of ~30 dB and a saturation power of at least three orders of magnitude larger than that of the best-reported JPAs. Such an amplifier may be promising for superconducting qubits and magnetic resonance applications.