Pure dephasing in flux qubits due to flux noise with spectral density scaling as 1/fα1/ f^\alpha

For many types of superconducting qubits, magnetic flux noise is a source of pure dephasing. Measurements on a representative dc superconducting quantum interference device (SQUID) over a range of temperatures show that $S_\Phi(f) = A^2/(f/1 \hbox{Hz})^\alpha$, where $S_\Phi$ is the flux noise spectral density, $A$ is of the order of 1 $\mu\Phi_0 \, \hbox{Hz}^{-1/2}$ and $0.61 \leq \alpha \leq 0.95$; $\Phi_{0}$ is the flux quantum. For a qubit with an energy level splitting linearly coupled to the applied flux, calculations of the dependence of the pure dephasing time $\tau_\phi$ of Ramsey and echo pulse sequences on $\alpha$ for fixed $A$ show that $\tau_\phi$ decreases rapidly as $\alpha$ is reduced. We find that $\tau_\phi$ is relatively insensitive to the noise bandwidth, $f_1 \leq f \leq f_2$, for all $\alpha$ provided the ultraviolet cutoff frequency $f_2 > 1/\tau_\phi$. We calculate the ratio $\tau_{\phi,E} / \tau_{\phi,R}$ of the echo ($E$) and Ramsey ($R$) sequences, and the dependence of the decay function on $\alpha$ and $f_2$. We investigate the case in which $S_\Phi(f_0)$ is fixed at the "pivot frequency" $f_0 \neq 1$ Hz while $\alpha$ is varied, and find that the choice of $f_0$ can greatly influence the sensitivity of $\tau_{\phi,E}$ and $\tau_{\phi,R}$ to the value of $\alpha$. Finally, we present calculated values of $\tau_\phi$ in a qubit corresponding to the values of $A$ and $\alpha$ measured in our SQUID.Comment: 7 pages, 8 figures, 1 tabl

Implications of heavy-ion-induced satellite x-ray emission. II. Production of K and L x rays by 0. 9 to 2. 6 MeV/u Ar ions in thick targets of V, Cu, Nb, Ta, and Pt

Cross sections are reported for x-ray production in targets of /sup 23/V, /sup 29/Cu, /sup 41/Nb, /sup 73/Ta, and /sup 78/Pt by /sup 40/Ar ions of 36.0, 56.4, 76.6, and 103 MeV. Because the targets were relatively thick, approx. 1 mg/cm/sup 2/, the data were corrected, using a novel approach, for projectile energy loss and x-ray attenuation in the targets. The cross sections so analyzed are compared with the predictions of the first Born approximation as well as with those of a more extensive treatment which includes energy loss, Coulomb deflection, perturbed stationary-state, and relativistic effects. The significant discrepancies between the data and this latter theory are atrributed primarily to the influence of multiple ionization on the x-ray emission probabilities

Multiple outer-shell ionization effect in inner-shell x-ray production by light ions

This article discusses multiple outer-shell ionization effect in inner-shell x-ray production by light ions

Detection and measurement of nuclear radiation

The technique of radiation characterization is reviewed, with particular emphasis on new methods and their practi-cal aspects. Each type of detector is discussed in terms of its principle of operation and its applicability to various problems in counting and spectrometry. Auxiliary electronic instrumentation and the function of each instrument are described in general terms. Other topics discussed include low-level counting, absolute counting, and the mounting of radioactive sources. (137 references.) (C.H.

Atomic Energy Commission Report MTA-31

From abstract: An automatic gamma-ray spectrometer for routine assays in radiochemical investigations has been constructed. Circuits are described for the automatic control of the pulse analyzer bias and automatic recording of the counting data. Typical gamma-ray spectra are shown as an indication of the perfomance obtained

Detection and Measurement of Nuclear Radiation

The technique of radiation characterization is reviewed, with particular emphasis on new methods and their practi-cal aspects. Each type of detector is discussed in terms of its principle of operation and its applicability to various problems in counting and spectrometry. Auxiliary electronic instrumentation and the function of each instrument are described in general terms. Other topics discussed include low-level counting, absolute counting, and the mounting of radioactive sources. (137 references.) (C.H.

Atomic Energy Commission Report MTA-37

From abstract: An electromechanical automatic count and control unit for a beta-ray spectrometer is described. The count control unit provides for constant or time limited recording of data and actuates an automatic stepping system which sweeps a well regulated motor generator power supply over 100 increments of focusing magnet current

Recovery and purification of nickel-63 from HFIR-irradiated targets

The production of large quantities of high-specific-activity [sup 63]Ni (>10 Ci/g) requires both a highly enriched [sup 62]Ni target and a long irradiation period at high neutron flux. Trace impurities in the nickel and associated target materials are also activated and account for a significant fraction of the discharged activity and essentially all of the gamma activity. While most of these undesirable activation products can be removed as chloride complexes during anion exchange, chromium, present at [sup 51]Cr, and scandium, present as [sup 46]Sc, are exceptions and require additional processing to achieve the desired purity. Optimized flowsheets are discussed based upon the current development and production experience

Detection and measurement of nuclear radiation /

Includes bibliographical references.Mode of access: Internet