A Chirality-Based Quantum Leap

Abstract

There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light-matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral-optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light-matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.

Keywords: chiral imprinting; chirality; electron transport; photoexcitation; probe microscopy; quantum biology; quantum information; quantum materials; spintronics.

Figure 1

Chiral experimenter’s space. The matter under study and the probe (e.g., electromagnetic fields) can be either chiral or nonchiral. We expect different interaction strengths and rules to be valid in each “box”. A third interaction axis points to the fact that matter–probe interactions could be classical (incoherent) (boxes 1–4) or, in principle, preserve coherences (boxes 5–8).

Figure 2

Spin-polarized charge transport in chiral-induced spin selectivity (CISS) devices. (a) Schematic of the device structure of a (Ga,Mn)As/polyalanines/Au vertical junction. (b) Junction conductance vs perpendicular magnetic field measured at a DC bias current of 100 μA. The garnet arrow indicates the direction of the (Ga,Mn)As magnetization, and the gold arrow represents the direction of the electron spin polarization. The black and red dashed arrows indicate the sweeping direction of the magnetic field. (c) ΔG_J as a function of bias current from I–V measurements at different fields (black squares) and MC measurements at different biases (red triangles). Blue line is a linear fit to the black squares. Adapted with permission from ref (40). Copyright 2020 American Chemical Society.

Figure 3

Spin-dependent photoelectron scattering of DNA hairpins. (a) Schematic depicting spin-dependent photoelectron scattering through self-assembled monolayers of DNA hairpins on ferromagnetic films, characterized by ultraviolet photoelectron spectroscopy. Spin-dependent ionization cross sections result in differential charging, physically manifested as substrate magnetization-dependent photoionization energies of the chiral organic films. (b,c) Spin-selective effects were only observed in short (∼1 helical turn) DNA hairpins that contained mercury bound at thymine–thymine mismatches due to enhanced molecular spin-orbit coupling. (d) Spin selectivity was reversed in DNA hairpins containing 7 mismatches and stoichiometric amounts of mercury ions, which was shown to invert the chirality of the helical hairpins. All panels reproduced with permission from ref (47). Copyright 2020 American Chemical Society.

Figure 4

Spin polarization of photoelectrons from Cu, Ag, and Au substrates transmitted through a monolayer of M hepta-helicene. (a) Structures of enantiomers. (b) Experimental setup for photoemission and Mott analyzer. (c) Green, blue, and red histograms (from top to bottom) represent excitation by clockwise (cw) circularly, linearly, and counterclockwise (ccw) circularly polarized light at λ = 213 nm, and thus emitting electrons slightly above the vacuum level of the systems. Adapted with permission from ref (50). Copyright 2018 American Chemical Society.

Figure 5

Chiral-induced spin selectivity effect and ferromagnetic substrates. (a) Experimental scheme and (b) topographic (top) and magnetic phase (bottom) images of chiral α-helical peptides adsorbed on perpendicularly magnetized substrates showing opposite magnetization induced by opposite enantiomers (left- and right-hand columns). Panels (a,b) reproduced with permission under a Creative Commons CC BY license from ref (36). Copyright 2017 Springer Nature. (c) Experimental scheme and (d) magnetization using NV center magnetometry. In (d), the top left image is a simulation of substrate magnetization after 4 h, and experiments show decreasing magnitude after 4 (top right), 8 (bottom left), and 12 (bottom right) h. Panels (c,d) Reproduced with permission from ref (59). Copyright 2021 American Chemical Society. (e) Experiment schematic and (f) measurement mechanism of atomic force microscopy (AFM)-based spin-exchange microscopy using chiral molecules. Panels (e)-(f) reproduced with permission from ref (60). Copyright 2019 John Wiley & Sons.

Figure 6

Interactions between chiral molecules and ferromagnetic (FM) surfaces. As a chiral molecule approaches the FM substrate, its charge polarization generates a spin polarization at the two ends of the molecule. For a specific enantiomer, the interaction between the magnetized surface and the molecule (circled in blue and red) follows a low-spin or a high-spin potential, depending on the direction of magnetization of the substrate. Reproduced with permission from ref (57). Copyright 2018 American Association for the Advancement of Science.

Figure 7

Temperature dependence of spin-dependent electron transport through the protein azurin. (a) Schematic of magnetoconductance device with wild-type azurin sandwiched between ferromagnetic and normal metal electrodes. (b) Magnetoresistance measured from 300 to 4 K. (c) Measurement scheme to detect photoinduced charge transfer between a ruthenium donor and copper acceptor groups and a ferromagnetic substrate. (d) Spin-independent photovoltage and spin polarization percentage as a function of temperature. (e) Model of vibronically activated spin-polarization. Adapted with permission from ref (64). Copyright 2021 American Chemical Society.

Figure 8

Evidence for allosteric long-range charge reorganization in proteins. (a) Fluorescence microscopy images of antibody–antigen binding to oppositely magnetized substrates. (b,c) Reaction kinetics of the binding interaction. (d) Schematic of the spin-valve-like behavior gating charge reorganization when antibodies are adsorbed on ferromagnetic substrates. Reproduced with permission from ref (67). Copyright 2020 by American Chemical Society.

Figure 9

Reaction scheme and chirality in electropolymerization. (a) Reaction scheme for the polymerization of 1-pyrenecarboxylic acids into polypyrene which exhibits a helical twist (see main text for more details). (b) Circular dichroism (CD) spectra for electrodes coated with polypyrene where a magnetic field was applied up (red) or down (blue) during electropolymerization. (c) Electrochemistry measurements on (S)- (black) or (R)-ferrocene (red) with the up (left) or down (right) polypyrene-coated working electrodes. Panels (a–c) reproduced with permission from ref (69). Copyright 2020 John Wiley and Sons. (d) Interaction scheme between a ferromagnetic electrode and chiral monomers. Panel (d) reproduced with permission from ref (70). Copyright 2020 American Chemical Society.

Figure 10

(a) Experimental scheme for magnetic conducting atomic force microscopy measurement of chiral perovskite thin films. (b–d) Current–voltage traces collected for thin films of lead–iodide perovskites containing chiral R-methylbenzylammonium (R-MBA), achiral phenylethylamine, and chiral S-methylbenzylammonium (S-MBA), respectively, as a function of tip-magnetization orientation. Reproduced with permission under a Creative Commons Attribution-NonCommercial License from ref (73). Copyright 2019 American Association for the Advancement of Science.

Figure 11

(a) Schematics of the Sagnac magneto-optic Kerr effect experiment at the interface of a chiral-hybrid organic–inorganic perovskite (HOIP) and NiFe substrate. (b) The change in Kerr signals with photoexcitation under positive and negative out-of-plane magnetic field. (c) Schematics of the chiral 2D perovskite/transition metal dichalcogenide heterostructure. (d) Polarization-resolved photoluminescence spectra of the heterostructure excited by a linearly polarized laser of 532 nm. (e) Schematics of a chiral-induced spin selectivity (CISS) spin-light-emitting diode. (f) Electroluminescence spectrum with CISS layer/CsPbI₃ heterostructures and a device image as inset. Panels (a,b) reproduced with permission from ref (76). Copyright 2020 American Chemical Society. Panels (c,d) reproduced with permission from ref (77). Copyright 2020 American Chemical Society. Panels (e,f) reproduced with permission from ref (79). Copyright 2021 American Association for the Advancement of Science.

Figure 12

(a) Schematics of crystal structures of CrNb₃S₆. (b) Schematics and electrical measurements of chiral-induced spin selectivity (CISS) and inverse CISS signals. Panels (a,b) reproduced with permission from ref (80). Copyright 2020 American Physical Society. (c) Schematics of crystal structures of a disilicide compound MSi₂ (M: transition metal). (d) Location variations of the CISS signals of NbSi₂ and TaSi₂. Panels (c,d) reproduced with permission from ref (81). Copyright 2021 American Physical Society.

Figure 13

(a) For a realistic peptide helix, a density functional theory-based Landauer approach including spin-orbit coupling (SOC) yields spin polarization as rather narrow peaks far from the Fermi energy (solid line in the plot, reported as junction magnetoresistance; using Perdew-Burke-Ernzerhof, PBE, functionals). (b) For a model helix of equidistant carbon atoms (capped by two hydrogens at each end), spin polarization over a broad energy range close to the Fermi energy is obtained, but it can be traced back to spin-orbit transfer from the gold electrodes rather than resulting from SO intrinsic to the helix (in the plot, the Fermi energy is between −5 eV and −4 eV for gold; using a B3LYP functional). Note that the exchange–correlation functional PBE (plot in (a)) features 0% Hartree–Fock exchange, while B3LYP (used on the right) has 20%, and that the absolute values of spin polarization depend on this exchange admixture. Importantly, the polarization changes sign when the helicity is inverted and increases with molecular length (plot in (b)). Panel (a) reproduced with permission from ref (90). Copyright 2018 American Chemical society. Panel (b) reproduced with permission from ref (53). Copyright 2020 American Chemical Society.

Figure 14

In the case of chiral molecules, induction, and dispersion forces encoding electric dipole–dipole interactions require additional modifications to account for exchange-mediated interactions related to the chiral-induced spin selectivity effect.

Figure 15

(a) The helical tube. Electrons are confined to a helical tube of radius R and pitch b, s is the position along the helix tube, and vectors n and t span the plane perpendicular to s. A term in the Hamiltonian acts as an effective Zeeman field rotating as a function of the position along the helix. (b) Transmission through an helix-shaped molecule in the presence of a dipole field. (Top left) In the presence of SOC, the amplitude of the (exact) electronic wave function in its tail (parametrized by ξ ≫ 1) grows as a function of the angular momentum. Moreover, the spin is aligned along the momentum direction (see inset), and as a consequence, the state has a well-defined helicity. (Top right) The increased amplitude deep inside the molecule gives rise to an enhanced transmission probability that grows with the angular momentum . The scattering matrix is derived for the exact wave function. This panel shows that the enhanced transmission for is accompanied by a spin polarization (inset). (Bottom left) Similar results were obtained using a tight binding calculation for a molecule with the same parameter but somewhat different length. (Bottom right) Deforming the molecule to have a larger pitch or radius helps spin polarization. All panels adapted with permission from ref (127). Copyright 2019 American Chemical Society.

Figure 16

(a) Schematics of the orbital polarization effect. (i) A chiral molecule is connected to two leads on each end and (ii) acts as both an orbital polarizer and (iii) an orbital filter. The half circles with arrows represent the orbital and thin arrows represent the spin. Adapted with permission from ref (130). Copyright 2021 Springer Nature. (b) Schematics of the description of the origin of the chiral-induced spin selectivity effect. The interface orbital magnetization is indicated by the blue arrow at a tilted angle. It interacts with two effective magnetic fields: the solenoid field and the spin-torque field. SOC: spin-orbit coupling. Adapted with permission from ref (131). Copyright 2021 American Chemical Society.

Figure 17

Spin-orbit interactions and spin selectivity for tunneling electron transfer in DNA. (a) Schematic of DNA molecule with orbitals for electron transport. The p_z orbitals are perpendicular to the base planes and coupled by V_ppπ Slater–Koster matrix elements. (b) Plot of spin asymmetry P_z as a function of scattering barrier length a and input momentum k. Adapted with permission from ref (141). Copyright 2020 American Physical Society.

Figure 18

(a) Scanning electron microscope (SEM) image of a platinum chiral nanohelix grown by focused ion beam induced deposition (FIBID) and a 3D representation of current oscillation induced by exciting on resonance for the right- and left-handed resonance modes. Adapted with permission from ref (183). Copyright 2015 American Chemical Society. (b) Strongly enhanced optical chirality density (C) theoretically predicted to be generated within plasmonic helices. Adapted with permission from ref (170). Copyright 2014 American Chemical Society. (c) SEM images of left- and right-handed planar chiral coupled nanorod antennas and experimentally measured chirality flux efficiency for each configuration. Adapted with permission from ref (178). Copyright 2018 American Chemical Society. (d) Optical chirality density enhancement, electric field enhancement, and circular dichroism (CD) calculated for pure left- and right-handed as well as racemic mixtures of plasmonic gammadion arrays. Adapted with permission from ref (181). Copyright 2018 American Chemical Society.

Figure 19

(a) Nanoparticles can enhance molecular circular dichrosim (CD) spectroscopy. A 75 nm radius silicon nanosphere is illuminated from below by λ = 625 nm circularly polarized light. The figure depicts the CD enhancement factor at a plane crossing the center of sphere. (b) When Kuhn’s dissymmetry factor is increased in the vicinity of a nanoparticle, the enantiomeric excess achievable in a photochemical reaction increases dramatically for a given extent of reaction. (Inset) Spatial distribution of dissymmetry factor enhancement for a 536 nm Si sphere at λ = 1391.82 nm. In the presence of a Si nanosphere, in a region where g ≈ 7, a 20% enantiomeric excess can be reached with a yield of 50% compared to the 1% achievable in the absence of the nanoparticle. Panel (a) adapted with permission from ref (205). Copyright 2013 American Physical Society. Panel (b) adapted with permission from ref (204). Copyright 2017 American Chemical Society.

Figure 20

(a) Scanning electron micrograph of a Si nanodisk array coated with a ca. 200 nm phenylalanine layer. (b,c) Experimentally measured circular dichrosim (CD) and extinction spectra of Si nanodisk sensor arrays functionalized with phenylalanine coatings. Panels (a–c) adapted with permission from ref (211). Copyright 2020 American Chemical Society. (d) Experimental schematic of fluorescence-detected circular dichroism (FDCD) using Si nanodisk arrays modified with self-assembled monolayers of chromophore-functionalized DNA molecules. (e) Experimentally measured FDCD and enhancement in optical chirality density for increasing disk sizes when functionalized with DNA monolayers. Panels (d,e) adapted with permission from ref (217). Copyright 2020 American Chemical Society.

Figure 21

(a) Schematic of the plasmonic nanoparticle–chiral molecule hybrid. The silver nanoparticle is surrounded by reporter Raman-active molecules, surrounded by a silica shell and has attached a chiral analyte. The middle plot shows surface enhanced resonant Raman spectra of d- and l-tryptophan bound to the benzotriazole-functionalized nanotag, which are identical as expected for the two enantiomeric systems. Surface enhanced Raman optical activity spectra in the presence of the two chiral enantiomers. Strong chiroptical responses in several signals are observed, demonstrating the chirality transfer phenomena. (b) Schematic of the model describing the chiral molecule–nanoparticle hybrid. Step 1: Circularly polarized light excites the plasmonic nanoparticle. Steps 2a and b: The plasmonically enhanced fields excite the chiral molecule, which backscatters light into the particle, producing a self-consistent chiral polarization of the plasmonic particle. Step 3: The chiral polarization of the chiral molecule–nanoparticle hybrid excites the nonchiral Raman-active reporter molecule. Step 4: The Raman-active molecule emits a surface-enhanced resonant Raman signal, which is different for left handed (M⁺) and right handed (M^–) circularly polarized incidence, creating a measurable Raman optical activity signal. Panel (a) adapted with permission from ref (17), based on work in ref (224). Copyright 2015 Springer Nature. Panel (b) adapted with permission from ref (225). Copyright 2020 American Chemical Society.

Figure 22

(a) Circular dichroism (CD) and optical absorption spectra for l-graphene quantum dot (l-GQD, red) and d-GQD (black) dispersions. (b) Schematic of the structures of d-GQD and l-GQD on a 3 nm QD. The rotation direction of the helices is opposite to the handedness of the edge ligands. (c) CD spectra of d-/l-cysteine functionalized MoS₂ after exfoliation. Similar results for d-/l-penicillamine were obtained (not shown here). (d) Diagram of the deformations generated by molecular functionalization of d-penicillamine inducing chirality on MoS₂ layers. (e,f) Frequency shifts of the d- and l-Cys-MoS₂ QDs/Cu²⁺ sensors exposed to (e) 5 mM d-Tyr and (f) 5 mM l-Tyr solution. Panels (a,b) adapted with permission from ref (227). Copyright 2016 American Chemical Society. Panels (c,d) adapted with permission from ref (235). Copyright 2018 American Chemical Society. Panels (e,f) adapted with permission from ref (248). Copyright 2018 American Chemical Society.

Figure 23

Conductance histograms for hundreds of single-peptide junctions collected in different scanning tunneling microscopy break junction experiments with Ni tips magnetized (a) down and (b) up for both left- and right-handed α-helical peptides. These peptides are composed of 22 amino acid residues bridges attached to gold substrates. Insets depict representative current vs pulling traces with well-defined single-molecule plateau features. Conductance values were extracted from Gaussian fits to the histograms. Adapted with permission from ref (107). Copyright 2017 John Wiley and Sons.

Figure 24

(a) Electron transfer and intersystem crossing pathways in a (D−χ–A) system, where k_CS is the charge separation rate constant, k_RP-ISC is the radical pair intersystem crossing rate constant, and k_CRS and k_CRT are the charge recombination rates via the singlet and triplet channels, respectively. (b) (D^•+–χ–A^•–) energy levels as a function of magnetic field for 2J > 0, D = 0. (c) (D^•+–χ–A^•–) energy levels in the high field limit with no CISS, where ω is the mixing frequency and the enhanced absorptive (a) and emissive (e) microwave-induced transitions are indicated. (d) (D^•+–χ–A^•–) energy levels with chiral-induced spin selectivity in which only |3⟩ is populated.

Figure 25

(a) Schematic of radical pair formation in donor–bridge–acceptor species and pulse sequence in a hypothetical out-of-phase electron spin–echo envelope modulation (OOP-ESEEM) electron paramagnetic resonance (EPR) experiment. (b) Calculated OOP-ESEEM signal from opposite enantiomers in a chiral radical pairs showing different phase shifts. Panels (a,b) adapted with permission from ref (329). Copyright 2021 American Chemical Society. (c) Proposed EPR and (d) Nuclear magnetic resonance (NMR) experiments to elucidate the role of chiral linkers in spin-dependent transfer in chiral donor–bridge–acceptor pairs. Panels (c,d) adapted with permission from ref (330). Copyright 2021 American Chemical Society.

Figure 26

(a) Time-resolved electron paramagnetic resonance spectrum of NDI–A₃G₁–Sd at 85 K, 100 ns after a 355 nm, 7 ns laser pulse (black trace) and its simulation (red trace). (b) Out-of-phase electron spin–echo envelope modulation (OOP-ESEEM) for NDI–A₂G_n–Sd hairpins. Experimental data are shown for NDI–A₂G₂–Sd (red), NDI–A₂G₃–Sd (blue), and NDI–A₂G₄–Sd (green). Simulated echo modulations (black) used to predict the SCRP distances listed for each hairpin based on the extracted dipolar coupling constant. (c) Cartoon of NDI–A₂G₂–Sd illustrating the rotation of the Sd end-cap necessary to achieve the measured radical pair distances between NDI^•– and Sd^•+. All panels adapted with permission from ref (318). Copyright 2019 American Chemical Society.

Figure 27

Conductance properties of a low-resistance (120 Ω) NbSe₂/Au junction after chemisorption of chiral molecules on the NbSe₂ flake (∼25 nm thick). (a) Temperature dependence of dI/dVvsV spectra showing a distinct zero-bias conductance peak (ZBCP) that vanishes at higher temperatures (but still below T_c). Inset: Illustration of a chiral-molecules/NbSe₂-flake/Au sample. (b) Temperature dependence of the conductance at zero bias with two transition temperatures marked by arrows: T_c = 7.2 K, where the zero bias conductance starts to rise due to the Andreev dome and 5.5 K where a zero bias conductance peak starts to appear. Inset: Optical image of the sample with the measurement scheme depicted. (c,d) Perpendicular (c) and parallel (d) magnetic field dependencies of the conductance spectrum, showing that in high magnetic fields, yet below the parallel and perpendicular critical fields (H_c2) of bulk NbSe₂, the zero-bias conductance peak vanishes, revealing an underlying gap. All panels adapted with permission from ref (339). Copyright 2019 American Chemical Society.

Figure 28

A schematic illustration of a “super chiral molecule”: a coupled chiral-molecule/quantum dot (QD) hybrid structure, for controlling and manipulating spin polarization and entanglement. The gate voltage is applied to change the QD structure for controlling spin polarization.

Figure 29

Chiral molecules could be used as interconnects or quantum information transducers that have a longer-range than dipolar-coupled spin buses.

Figure 30

Effects of light on chiral molecules through the Floquet approach to achieve stretch and spectral engineering. (a) Molecules can be made to stretch or contract by impinging light (b) modulating the spin-orbit coupling. (c) Spectrum normalized by base pair to base pair overlap strength as a function of spin state (s), transport direction (ν) and pseudospin quantum (σ) vs the normalized frequency (ξ) of impinging light. Adapted with permission under a Creative Commons CC BY-NC 4.0 License from ref (137). Copyright 2018 Swiss Chemical Society.

Figure 31

(a) Tubulin proteins (left, scale bar ∼5 nm) polymerize into microtubules (right, scale bar ∼25 nm). (b) Highly ordered arrays of tryptophan amino acids (left, in blue) absorb ultraviolet radiation collectively with strong transition dipole moments (right, in red, scale bar ∼25 nm). Reproduced with permission under a Creative Commons Attribution 3.0 License from ref (406). Copyright 2019 IOP Publishing Ltd.

Figure 32

Quantum probability of finding the collective excitonic state on a single tryptophan residue of a microtubule segment is shown for an extended superradiant state (top row) and subradiant state (bottom row) in lateral view (left column) and in cross section (right column). Microtubule segment consists of 100 spirals (>800 nm) with 10,400 tryptophan residues. Reproduced with permission under a Creative Commons Attribution 3.0 License from ref (406). Copyright 2019 by IOP Publishing Ltd.