Decoherence is a process in quantum mechanics where a quantum system interacts with its environment, leading to the loss of coherence and the emergence of classical behavior. It is a fundamental challenge in maintaining quantum effects on macroscopic scales.
When it comes to quantum tunneling, which is the phenomenon where a particle can pass through a classically forbidden energy barrier, decoherence is known to play a role. Decoherence tends to suppress quantum interference effects, making the probability of tunneling lower for macroscopic objects compared to microscopic particles.
While it is true that calculating the precise impact of decoherence on the probability of macroscopic quantum tunneling is challenging, the claim that decoherence does not completely prevent such tunneling is based on theoretical considerations and experimental evidence. Here are a few reasons why physicists make this claim:
Scaling arguments: The effects of decoherence scale with the size and complexity of the system. As a system becomes larger and more complex, the rate of decoherence generally increases. However, it does not necessarily mean that tunneling is completely suppressed. The specific conditions, such as the barrier height, width, and the coupling strength to the environment, can influence the extent of decoherence and its impact on tunneling. Thus, it is reasonable to expect that there might be regimes where macroscopic tunneling can still occur despite decoherence.
Experimental observations: Experimental evidence supports the existence of macroscopic quantum phenomena, including tunneling, in certain systems. For instance, superconducting devices called Josephson junctions exhibit macroscopic quantum tunneling effects that have been observed and studied in the laboratory. These observations suggest that, under certain conditions, macroscopic objects can exhibit quantum behavior even in the presence of decoherence.
Theoretical frameworks: Various theoretical frameworks, such as the theory of open quantum systems and the theory of quantum dissipation, provide mathematical models to describe the interaction between a quantum system and its environment. While calculating precise decoherence effects for macroscopic tunneling can be complex, these frameworks offer insights into how the interplay of system-environment interactions affects the probability of tunneling.
It is important to note that the study of decoherence and its impact on macroscopic quantum phenomena is an active area of research. The field continues to advance, and researchers are developing theoretical models and conducting experiments to further understand the conditions under which macroscopic quantum tunneling can occur in the presence of decoherence.
Overall, while the exact quantitative impact of decoherence on macroscopic quantum tunneling may not be fully calculable, the claim that decoherence does not completely prevent such tunneling is supported by theoretical considerations, experimental observations, and ongoing research in the field.