Macroscopic entanglement between wave-packets at finite temperature

Abstract: We investigate entanglement between collective operators of two wave-packets of finite spectral bandwidth, in two different approximations of the Multimode Parametric-Down Conversion (MPDC) process: the pairwise and the one-to-all interaction patterns. For collective operators we choose the macroscopic amplitudes of each wave-packet defined by the Fourier Transform of their microscopic mode amplitudes. This approach intends, to respond to realistic experimental conditions, where measurements apparatuses may not resolve single microscopic mode amplitudes but rather the collective amplitude of the wave-packets. To quantify the bipartite macroscopic entanglement we use the logarithmic negativity. We relate the time dependent degree of macroscopic entanglement with the complexity (number of modes and interaction pattern) and the temperature of the system. Our results show that the macroscopic entanglement increases linearly with the number of micro-modes in the case of the one-to-all interaction, while in the pairwise interaction it is constant. Moreover, in the one-to-all} pattern the birth time of entanglement and the critical temperature decrease with increasing the number of micro-modes. We draw the graphs associated with the two interaction patterns and related the degree of collective entanglement with the connectivity and the index of each vertex (mode) of the graph. We conclude that quantum information and computation tasks may be achieved more efficiently by manipulating appropriated collective operators in some macroscopic systems, then by using their microscopic counterparts.