Potential coexistence of exciton and fermion-pair condensations

2020

Phys. Rev. A

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The computation of strongly correlated quantum systems is challenging because of its potentially exponential scaling in the number of electron configurations. Variational calculation of the two-electron reduced density matrix (2-RDM) without the many-electron wave function exploits the pairwise nature of the electronic Coulomb interaction to compute a lower bound on the ground-state energy with polynomial computational scaling. Recently, a dual-cone formulation of the variational 2-RDM calculation was shown to generate the ground-state energy, albeit not the 2-RDM, at a substantially reduced computational cost, especially for higher N -representability conditions such as the T2 constraint. Here we generalize the dual-cone variational 2-RDM method to compute not only the ground-state energy but also the 2-RDM. The central result is that we can compute the 2-RDM from a generalization of the Hellmann-Feynman theorem. Specifically, we prove that in the Lagrangian formulation of the dual-cone optimization the 2-RDM is the Lagrange multiplier. We apply the method to computing the energies and properties of strongly correlated electrons-including atomic charges, electron densities, dipole moments, and orbital occupations-in an illustrative hydrogen chain and the nitrogen-fixation catalyst FeMoco. The dual variational computation of the 2-RDM with T2 or higher N -representability conditions provides a polynomially scaling approach to strongly correlated molecules and materials with significant applications in atomic and molecular and condensed-matter chemistry and physics.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dual-cone variational calculation of the two-electron reduced density matrix

2020

Phys. Rev. A

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“…It may be possible to create materials that conduct both electric current and exciton excitation energy through the realization a single quantum state that simultaneously demonstrates properties of two different condensates-one composed of "Cooper" (particleparticle) pairs and the other composed of excitons (particle-hole pairs) [1]. Bose-Einstein condensation allows for multiple bosons aggregating in a single quantum state [2,3] at sufficiently low temperatures, resulting in the superfluidity of the constituent bosons [4,5].…”

Section: Introductionmentioning

confidence: 99%

Entangled phase of simultaneous fermion and exciton condensations realized

Sager

2022

Phys. Rev. B

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Fermion-exciton condensates (FECs)-computationally-and theoretically-predicted states that simultaneously exhibit character of superconducting states and exciton condensates-are novel quantum states whose properties may involve a hybridization of superconductivity and the dissipationless flow of energy. Here, we exploit prior investigations of superconducting states and exciton condensates on quantum devices to identify a tuneable quantum state preparation entangling the wavefunctions of the individual condensate states. Utilizing this state preparation, we prepare a variety of fermion-exciton condensate states on quantum computers-realizing strongly-correlated FEC states on current, noisy intermediate-scale quantum devices-and verify the presence of the dual condensate via post-measurement analysis. This confirmation of the previously-predicted condensate state on quantum devices as well as the form of its wavefunction motivates further theoretical and experimental exploration of the properties, applications, and stability of fermion-exciton condensates.

“…Exciton condensation-a Bose-Einstein condensation of particle-hole pairs into a single quantum statehas generated considerable experimental and theoretical interest [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] due to the resultant superfluidity [20][21][22][23] of the constituent excitons (particle-hole pairs) allowing for the dissipationless transport of energy 24,25 , which presents the possibility for uniquely energy efficient materials. Further, the greater binding energy and lesser mass of excitonic quasiparticles relative to particle-particle Cooper pairs indicates that exciton condensation should occur at higher temperatures 26 relative to the temperatures at which traditional superconductivity-i.e., the condensation of particle-particle pairs into a single quantum state [27][28][29][30] -occurs.…”

Section: Introductionmentioning

confidence: 99%

“…Specifically, van der Waal heterostructures 4,33,39,43 as well as graphene bilayers 17,31,44 demonstrate promise in the search for higher-temperature exciton condensate phases, with the tuneability of electronic states afforded by twisting graphene layers relative to each other being particularly of interest in recent literature 35,41 . a) Electronic mail: damazz@uchicago.edu Small, molecularly-scaled systems have also been revealed to support exciton condensation via theoretical explorations utilizing a signature of such condensation found in the modified particle-hole reduced density matrix (RDM) [8][9][10][11] . These molecular systems are able to be treated using theoretical approaches at lower computational costs and can be used as an analog for similar larger-scaled systems; moreover, molecular-scaled exciton condensation in and of itself may have potential applications in the design of more energy-efficient molecular-structures and devices.…”

Section: Introductionmentioning

confidence: 99%

Beginnings of exciton condensation in coronene analog of graphene double layer

Sager

Schouten

The Journal of Chemical Physics

2022

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Exciton condensation, a Bose–Einstein condensation of excitons into a single quantum state, has recently been achieved in low-dimensional materials including twin layers of graphene and van der Waals heterostructures. Here, we computationally examine the beginnings of exciton condensation in a double layer composed of coronene, a seven-benzene-ring patch of graphene. As a function of interlayer separation, we compute the exciton population in a single coherent quantum state, showing that the population peaks around 1.8 at distances near 2 Å. Visualization reveals interlayer excitons at the separation distance of the condensate. We determine the exciton population as a function of the twist angle between two coronene layers to reveal the magic angles at which the condensation peaks. As with previous recent calculations showing some exciton condensation in hexacene double layers and benzene stacks, the present two-electron reduced-density-matrix calculations with coronene provide computational evidence for the ability to realize exciton condensation in molecular-scale analogs of extended systems such as the graphene double layer.