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Semiconductor moiré superlattices provide a versatile platform to engineer quantum solids composed of artificial atoms on moiré sites. Previous studies have mostly focused on the simplest correlated quantum solid—the Fermi-Hubbard model—in which intra-atom interactions are simplified to a single onsite repulsion energyU. Here we report the experimental observation of Wigner molecular crystals emerging from multielectron artificial atoms in twisted bilayer tungsten disulfide moiré superlattices. Using scanning tunneling microscopy, we demonstrate that Wigner molecules appear in multielectron artificial atoms when Coulomb interactions dominate. The array of Wigner molecules observed in a moiré superlattice comprises a crystalline phase of electrons: the Wigner molecular crystal, which is shown to be highly tunable through mechanical strain, moiré period, and carrier charge type. 

Abstract Voice-activated commands have become a key feature of popular devices such as smartphones, home assistants, and wearables. For convenience, many people configure their devices to be ‘always on’ and listening for voice commands from the user using a trigger phrase such as “Hey Siri,” “Okay Google,” or “Alexa.” However, false positives for these triggers often result in privacy violations with conversations being inadvertently uploaded to the cloud. In addition, malware that can record one’s conversations remains a signifi-cant threat to privacy. Unlike with cameras, which people can physically obscure and be assured of their privacy, people do not have a way of knowing whether their microphone is indeed off and are left with no tangible defenses against voice based attacks. We envision a general-purpose physical defense that uses a speaker to inject specialized obfuscating ‘babble noise’ into the microphones of devices to protect against automated and human based attacks. We present a comprehensive study of how specially crafted, personalized ‘babble’ noise (‘MyBabble’) can be effective at moderate signal-to-noise ratios and can provide a viable defense against microphone based eavesdropping attacks.