The Pauli exclusion principle governs the fundamental structure and function of fermionic systems from molecules to materials. Nonetheless, when such a fermionic system is in a pure state, it is subject to additional restrictions known as the generalized Pauli constraints (GPCs). Here we verify experimentally the violation of the GPCs for an open quantum system using data from a superconductingqubit quantum computer. We prepare states of systems with threetoseven qubits directly on the quantum device and measure the onefermion reduced density matrix (1RDM) from which we can test the GPCs. We find that the GPCs of the 1RDM are sufficiently sensitive to detect the openness of the 3to7 qubit systems in the presence of a singlequbit environment. Results confirm experimentally that the openness of a manyfermion quantum system can be decoded from only a knowledge of the 1RDM with potential applications from quantum computing and sensing to noiseassisted energy transfer.
Molecular simulations generally require fermionic encoding in which fermion statistics are encoded into the qubit representation of the wave function. Recent calculations suggest that fermionic encoding of the wave function can be bypassed, leading to more efficient quantum computations. Here we show that the twoelectron reduced density matrix (2RDM) can be expressed as a unique functional of the unencoded
 Award ID(s):
 2035876
 NSFPAR ID:
 10360374
 Publisher / Repository:
 IOP Publishing
 Date Published:
 Journal Name:
 New Journal of Physics
 Volume:
 23
 Issue:
 11
 ISSN:
 13672630
 Page Range / eLocation ID:
 Article No. 113037
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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Abstract 
Stateoftheart manybody wave function techniques rely on heuristics to achieve high accuracy at an attainable computational cost to solve the manybody Schrödinger equation. By far, the most common property used to assess accuracy has been the total energy; however, total energies do not give a complete picture of electron correlation. In this work, we assess the von Neumann entropy of the oneparticle reduced density matrix (1RDM) to compare selected configuration interaction (CI), coupled cluster, variational Monte Carlo, and fixednode diffusion Monte Carlo for benchmark hydrogen chains. A new algorithm, the circle reject method, is presented, which improves the efficiency of evaluating the von Neumann entropy using quantum Monte Carlo by several orders of magnitude. The von Neumann entropy of the 1RDM and the eigenvalues of the 1RDM are shown to distinguish between the dynamic correlation introduced by the Jastrow and the static correlation introduced by determinants with large weights, confirming some of the lore in the field concerning the difference between the selected CI and Slater–Jastrow wave functions.

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Key points Gap junctions formed by different connexins are expressed throughout the body and harbour unique channel properties that have not been fully defined mechanistically.
Recent structural studies by cryo‐electron microscopy have produced high‐resolution models of the related but functionally distinct lens connexins (Cx50 and Cx46) captured in a stable open state, opening the door for structure–function comparison.
Here, we conducted comparative molecular dynamics simulation and electrophysiology studies to dissect the isoform‐specific differences in Cx46 and Cx50 intercellular channel function.
We show that key determinants Cx46 and Cx50 gap junction channel open stability and unitary conductance are shaped by structural and dynamic features of their N‐terminal domains, in particular the residue at the 9th position and differences in hydrophobic anchoring sites.
The results of this study establish the open state Cx46/50 structural models as archetypes for structure–function studies targeted at elucidating the mechanism of gap junction channels and the molecular basis of disease‐causing variants.
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