Measuring the measurement problem: controlling decoherence with measurement duration in molecular MCB junctions

TL;DR

This study investigates how measurement duration affects quantum coherence in molecular MCB junctions within the THF partially wet phase, demonstrating that the observed quantum versus classical behavior depends on the integration time $\tau_m$ relative to the decoherence time $\tau_c$. Framed as an enclosed open quantum system with non-Markovian information exchange, the work shows that the ratio $\tau_m/\tau_c$ governs whether IV curves display interference-band structures or a single averaged response. Experimentally, varying $\tau_m$ between $640\mu$s and $20$ms reveals a transition from coherent to incoherent behavior and a characteristic four-group data pattern, indicating rich dynamics beyond simple noise. The results establish measurement duration as a practical knob for probing decoherence in ambient-condition molecular devices and highlight the coexistence of multiple quantum effects (qe1, qe2) in these systems, with implications for design and control of molecular-scale quantum technologies.

Abstract

We investigate the influence of the measurement duration on quantum coherence in molecular mechanically controlled break junctions operating in a tetrahydrofuran (THF) partially wet phase. These systems represent a distinct class of enclosed open quantum systems with unusually long decoherence times at ambient conditions, on the order of 1-20 ms. By tuning the integration time of the current measurement in current-voltage (IV) characteristics, relative to the decoherence time, we observe a transition from quantum interference patterns, manifested as structured bands of data points, to classical behavior characterized by a single averaged response. This demonstrates that the duration of a measurement acts as a controllable parameter for probing quantum behavior in molecular junctions, offering new insights into decoherence dynamics in quantum mechanics.

Figures (8)

• Figure 1: Schematic of a double scan consisting of 2N measurements, $\text{N}=1000$. A measurement consists of an integration time $\tau_m$ and a delay time $\tau_\text{delay}$. During $\tau_m$ the total charge that flows through the junction is integrated. During $\tau_\text{delay}$ the measurement current is calculated and stored, it also serves as some settling time.
• Figure 2: A characteristic IV curve from BBA1 where the measurement time is toggled between $\tau_m=20ms$ and $\tau_m=640µs$, indicating the sensitivity of quantum coherence in relation to the measurement time.
• Figure 3: First IV curve from BBA2 showing a spiky baseline with a superimposed finite bandwidth. Inset: four interleaved groups, 1mV per step, same color separation of 4mV.
• Figure 4: A section of fig. \ref{['fig:fig3']}, highlighting alternation of group colors between band edges.
• Figure 5: Second IV curve from BBA2 with a consistent bandwidth and clear repetitive structure, visible in both the main panel and inset.