According to a proposal, a phenomenon associated with excitation of quasi- particles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves.
The devices in question are single- Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron).
Experiments have shown that depending on the parameters of the device, quasiparticles in the form of “broken” Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called “poisoning.” Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal.
In a device according to the proposal, this poisoning would be turned to advantage. Depending on the wavelength, an antenna or other component would be used to couple radiation into the reservoir, wherein the absorption of photons would break Cooper pairs, thereby creating quasiparticles that, in turn, would tunnel to the island, creating a 1-e signal. On the basis of conservative estimates of device parameters derived from experimental data and computational simulations that fit the data, it has been estimated that the noise equivalent power of a device according to the proposal could be as low as 6 × 10–22 W/Hz1/2. It has also been estimated that the spectroscopic resolution (photon energy ÷ increment of photon energy) of such a device in visible light would exceed 100.
This work was done by Pierre Echternach and Peter Day of Caltech for NASA’s Jet Propulsion Laboratory. NPO-41936
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Using Quasiparticle Poisoning To Detect Photons
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Overview
The document titled "Using Quasiparticle Poisoning to Detect Photons" from NASA's Jet Propulsion Laboratory (JPL) discusses a novel approach to photon detection utilizing quasiparticle poisoning in superconducting devices. This technique aims to enhance sensitivity in detecting single photons, particularly in the far-infrared and sub-millimeter frequency ranges, which are crucial for various astrophysical missions.
The core concept revolves around exploiting the extreme sensitivity of superconducting single electron devices to quasiparticle excitations caused by pair-breaking radiation. When radiation is absorbed, it breaks Cooper pairs in the superconducting material, generating quasiparticles that can tunnel into a superconducting island, creating a detectable signal. The document outlines the theoretical framework and experimental data supporting this approach, including the calculation of Noise-Equivalent Power (NEP), which estimates the minimum detectable power levels. The proposed NEP of 6x10^-22 W/Hz^(1/2) indicates the potential for high sensitivity in photon detection.
The technology is particularly relevant for missions like BLISS-SPICA and the SAFIR interferometer, which require advanced detector sensitivity for observing faint astronomical signals. The document emphasizes the capability of these detectors to provide energy-resolved imaging and low-resolution spectroscopy, which are essential for applications in astrobiology, such as searching for life signatures on extrasolar planets.
The Single Cooper Pair Box (SCB) is highlighted as a key component in this detection system. It consists of a small superconducting island connected to a reservoir through a tunnel junction, allowing for the measurement of charge states influenced by quasiparticle tunneling. The expected charge response exhibits a staircase pattern, which can be altered by the presence of quasiparticles, leading to a 1-e periodic signal instead of the ideal 2-e periodicity.
Overall, the document presents a promising advancement in photon detection technology, leveraging quasiparticle dynamics to achieve unprecedented sensitivity. This innovation not only enhances the capabilities of current astrophysical instruments but also opens new avenues for research in various scientific fields, including astrophysics and prebiotic chemistry. The findings underscore JPL's commitment to developing cutting-edge technologies that can significantly impact our understanding of the universe.
