  Evolution of the energy landscape during physical aging of glassy materials
can be understood from the frequency and strain dependence of the shear modulus
but the non-stationary nature of these systems frustrates investigation of
their instantaneous underlying properties. Using a series of time dependent
measurements we systematically reconstruct the frequency and strain dependence
as a function of age for a repulsive colloidal glass undergoing structural
arrest. In this manner, we are able to unambiguously observe the structural
relaxation time, which increases exponentially with sample age at short times.
The yield stress varies logarithmically with time in the arrested state,
consistent with recent simulation results, whereas the yield strain is nearly
constant in this regime. Strikingly, the frequency dependence at fixed times
can be rescaled onto a master curve, implying a simple connection between the
aging of the system and the change in the frequency dependent modulus.
