According to some aspects, a method is provided of operating a circuit quantum electrodynamics system that includes a physical qubit dispersively coupled to a quantum mechanical oscillator, the method comprising applying a first electromagnetic pulse to the physical qubit based on a number state of the quantum mechanical oscillator, wherein the first electromagnetic pulse causes a change in state of the quantum mechanical oscillator, and applying, subsequent to application of the first electromagnetic pulse, a second electromagnetic pulse to the quantum mechanical oscillator that coherently adds or removes energy from the quantum mechanical oscillator.

Systems and methods for forming a compact gas sensor include using a lithographically fabricated high Q resonator coupled to at least one of a Gunn diode and an IMPATT diode. The resonator may include a plurality of cavities filled with a sample gas. A detector coupled to the resonator may measure the amplitude of the emitted mm wave radiation.

A high frequency electromagnetic radiation generation device is disclosed that includes a high voltage input, a nonlinear transmission line, an antenna, and a pulse recirculating circuit. In some embodiments, the high voltage input may be configured to receive electrical pulses having a first peak voltage that is greater than 5 kV, and/or may be electrically coupled with the nonlinear transmission line. The antenna may be electrically coupled with the nonlinear transmission line and/or may radiate electromagnetic radiation at a frequency greater than 100 MHz about a voltage greater than 5 kV. The pulse recirculating may be electrically coupled with the high voltage input and the antenna. The pulse recirculating circuit may include a diode; a low pass filter; and a delay line. In some embodiments, unradiated energy from the antenna is directed through the pulse recirculating circuit to the nonlinear transmission line with a delay of less than 100 ns.