Leggett–Garg Tests Under Fundamental Decoherence: The Measurable Window Computed for Mesoscopic Systems

This paper computes the measurement-interval window in which a Leggett–Garg test can still reveal quantum behaviour when the system undergoes exponential decoherence. With a decoherence rate of one per second, intervals must remain below 0.405 seconds to preserve the adopted violation margin; at one hundred per second the window shrinks to 4.050e-03 seconds, while at one hundredth per second it opens to 40.50 seconds. The window scales inversely with the rate, so a Leggett–Garg experiment measures, in effect, the product of rate and interval. Fundamental decoherence at Planck-suppressed levels would leave the window wide open for all mesoscopic systems considered; environmental rates are what close it in practice. The study is simulated and computed from stated assumptions; it is not a measurement.