Sources of Decoherence in the Transmon Qubit.

Here we discuss a new type of superconduting qubit known as the transmon, a Cooper Pair Box in the high E$_{j}$/E$_{c}$ limit. This qubit offers insensivity to 1/f noise in charge while maintaining sufficient anharmonicity to be treated as a two level system. In this talk we consider other experimentally important sources of dephasing and relaxation including: substrate/dielectric loss, flux coupling through the SQUID loop, radiation to parasitic modes, vortices, phonons, and quasiparticles. Order of magnitude estimates for these sources of decoherence indicate that T$_{1 }$and T$_{2}$ coherence times of at least 10 $\mu $s should be attainable.