Optical Interferometer with High Frequency Photon Counter

V. I. Shnyrkov, Wu Yangcao, A. A. Soroka +2 more

Various types of single-photon counters operating in infrared, ultraviolet, and optical wavelength ranges are successfully used to study electromagnetic fields, analyze radiation sources, and solve problems in quantum informatics. However, their operating principles become ineffective at millimeter band, S-band, and ultra-high frequency bands of wavelengths due to the decrease in quantum energy by 4–5 orders of magnitude. Josephson circuits with discrete Hamiltonians and qubits are a good foundation for the construction of single-photon counters at these frequencies. This paper presents a frequency-tuned microwave photon counter based on a single-junction superconducting quantum interferometer and flux qutrit. The control pulse converts the interferometer into a two-level system for resonance absorption of photons. Decay of the photon-induced excited state changes the magnetic flux in the interferometer, which is measured by a SQUID magnetometer. Schemes for recording the magnetic flux using a DC SQUID or ideal parametric detector, based on a qutrit with high-frequency excitation, are discussed. It is shown that the counter consisting of an interferometer with a Josephson junction and a parametric detector demonstrates high performance and is capable of detecting single photons in a microwave band.

P. Hariharan

Andrii P. Shapovalov, Volodymyr E. Shaternik, Oleg G. Turutanov +2 more

The nonhysteretic mode of a RF SQUID with a MoRe–Si(W)–MoRe Josephson junction is analyzed in order to detect the states of a single-photon counter based on a superconducting quantum interferometer with a discrete Hamiltonian. The absorption of a photon with 10 GHz frequency brings the counter to the excited level causing tunnelling into the adjacent potential well and a change in the magnetic flux in the interferometer, which can be detected by the SQUID magnetometer. Measurement of a quantum system requires minimization of the back action of the signal read-out channel at the counter, high sensitivity, and speed of the magnetometer. The MoRe–Si(W)–MoRe contacts are optimized for various concentrations of tungsten (W) in silicon (Si) and barrier layer thickness. It is shown that using MoRe–Si(W)–MoRe contacts with a tungsten concentration of approximately 11% for the RF SQUID at excitation frequencies of ∼1 GHz makes it practically an ideal parametric upward frequency shifter with noise determined by the cooled amplifier.

Ricardo Asch Campos

V. I. Shnyrkov, Wu Yangcao, Oleg G. Turutanov +2 more

Single-photon detectors are crucial elements of prospective quantum devices and techniques such as quantum communication systems, quantum computers, quantum radars, astrophysical detectors, etc. The detection of individual photons in microwave range is a much larger challenge as compared to that of in optics due to the quanta energy difference of 4 to 5 orders of magnitude which requires a quite different approach. So "artificial atoms" with discrete energy spectrum such as superconducting qubits are used here exploiting resonance transitions between their quantum states. A scheme incorporating a flux qubit with controllable spectrum as a single photon counter for 3-12 GHz range and weak continuous readout circuit based on rf superconducting quantum interferometer (SQUID) with UHF pumping is proposed and analyzed. High SQUID pumping frequency (about 500 MHz) along with using cooled microwatt HEMT preamplifier provides the measurement frequency band of up to 30 MHz while substantially diminishing the back-action effect.