We demonstrate that decay interference from the two upper levels of a four-level system can lead to loss-free propagation of a single, short laser pulse through an absorbing medium. In contrast to recent investigations of loss-free propagation in three-level media, no second coupling laser pulse is required. [S0031-9007(99) PACS numbers: 42.50. Gy, 42.50.Md, Dispersion and absorption properties of multilevel media can be modified through the introduction of a second, or coupling, laser pulse. The coherent interaction between the laser fields and the medium can result in phenomena such as electromagnetically induced transparency and matched pulse propagation [1] and the creation and propagation of "adiabatons" [2-4], a general class of solitonlike pulses that occur in adiabatically evolving systems [5]. Other remarkable properties have also been discussed [6][7][8][9][10][11][12]. Experimental investigations of adiabatons have been performed by Harris and co-workers [13]. As discussed by Eberly and co-workers [14], many of the above phenomena are related to coherent population trapping and the creation of "dark states" [15]. If the laser fields are applied adiabatically [5], then the medium can, under trapping conditions, establish a dark state leading to transparency in the medium.In the above mentioned processes it is crucial to have at least two laser pulses as both are used to create the necessary coherence. In this Letter we show that interference between decay channels can make a medium transparent to a single, short laser pulse. In this scheme interference inherent in the decay is exploited so that no coupling laser field is required for transparency. This type of interference was used in the original proposal of Harris [16] for lasing without inversion and has attracted much attention with regard to fluorescence quenching and related phenomena [17][18][19][20]. As in the theory of adiabatons our scheme also relies on the adiabatic evolution of a dark state of the system depicted in Fig. 1.In this Letter we focus on the case of an atomic medium and the decay process we consider is spontaneous emission. It should be emphasized that our analysis can be equally applied to other systems where such interference exists. Examples include spontaneous emission in molecules [21], processes involving autoionizing resonances [22], and semiconductor quantum well systems where the decay occurs via tunneling processes [23,24].We begin our analysis with the Maxwell-Schrödinger equations of motion for the system of Fig. 1. The wave function of the system is first expanded in terms of the field-free atomic states multiplied by the corresponding space and time-dependent amplitudes c m ͑z, t͒ (m 0, 1, 2) and c 3,k ͑z, t͒ of, respectively, the atomic and vacuum amplitudes. The laser pulse is taken to propagate in the z direction. Then c 3,k ͑z, t͒ is formally eliminated and the Weisskopf-Wigner theory of spontaneous emission applied. The result is the following set of equations in the rotating wave and the slowly varying enve...