Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Chinese Physics B

Coherently manipulating triplet-exciton qubit by circularly polarized laser

Longlong Zhang, Hongwei 宏伟 Li 李, Zhenyu 振宇 Xu 徐, Mengze Tao, Rui Chen, Yingqi Ma

Published Oct 17, 2025• 0 citations
Publisher

Abstract

Abstract We theoretically propose a scheme for the coherent manipulation of a single qubit, which is constructed using the self-trapped triplet exciton (STTE) in FM/polymer/FM sandwich. The STTE serves as a quantum dot, comprising two degenerate triplet states with opposite magnetizations, thereby forming the qubit’s subspace. We demonstrate that the spin state of this qubit can be coherently manipulated by applying an external circularly polarized laser (CPL) to form the Floquet state. The manipulation exhibits significant helicity dependence: when the CPL’s angular momentum is antiparallel to the STTE’s spin orientation, the STTE undergoes Rabi oscillations between the |↑↑〉 and |↓↓〉 state, corresponding to a π -rotation around the x -axis on the Bloch sphere. Conversely, when the CPL’s angular momentum is parallel to the STTE’s spin orientation, the STTE remains unresponsive to the CPL. Two-axis coherent control of the STTE qubit can be potentially realized by additionally applying a static magnetic field B z . Our work provides a theoretical perspective for realizing the coherent manipulation of a qubit in organic devices.

DOI
10.1088/1674-1056/ae1450

Related papers

Coherent control of quantum dot excitons using ultra-fast optical techniques: the role of acoustic phonons

A. J. Ramsay, A. M. Fox

Introduction Quantum dots are often referred to as artificial atoms, since they trap carriers in discrete energy-levels due to the nanoscale three-dimensional finite potential energy well they provide. As such, dots exhibit a coherent light–matter interaction that is similar to an atom. This is evidenced by observations of atom–optics phenomena such as Rabi oscillations [43, 26], power broadening [27], Autler–Townes doublet [14, 42], Mollow triplet [42, 8], and coherent population trapping [6]. In this chapter, Rabi rotation measurements are used to examine how an exciton transition deviates from an ideal two-level atom due to its interaction with a reservoir of phonons. The neutral exciton transition may be regarded as a two-level system, or qubit, composed of the crystal ground-state ∣0〉 and a single electron-hole pair ∣ X 〉. The state-vector of a qubit can be described as a pseudo spin-half. When an oscillating electro-magnetic field resonantly excites the two-level transition it drives an oscillation in the population inversion known as a Rabi oscillation. This results from the oscillations of the driving field and the dipole of the two-level system being synchronous, such that in its rotating frame, the driving field acts as a static magnetic field that causes the pseudo-spin to rotate. Coherent control of the pseudo-spin can be achieved by applying well-defined driving fields, enabling the preparation, and manipulation of superposition states. Such coherent control concepts have found widespread use in electron spin, and nuclear magnetic resonance spectroscopy.

Cambridge University Press eBooks•Jul 19, 2012•0 citations

Optical Coherent Control of a Single Charged Indium Arsenide Quantum Dot.

Katherine Truex

Optically driven self-assembled quantum dots are leading candidates for use in quantum computers because of their potential for high speed gate operations and relatively compact design. In this approach, each dot is charged with a single electron whose spin serves as the quantum bit (qubit). This thesis addresses the need for a universal set of gates to physically implement quantum computing and discusses initial steps toward spin-photon entanglement. Both are addressed through coherent control of the spin state in a magnetic field with optical pulses. This work experimentally demonstrates coherent rotations of the electron spin. First, the electron spin is rotated at up to 0.5 terahertz about the optical axis by a detuned picosecond optical pulse. The rotation occurs via a nearly resonant stimulated spin-flip Raman process involving a negatively charged exciton (trion). Second, rotation about an orthogonal axis is demonstrated due to electron spin precession about the magnetic field between two detuned optical pulses. The magnitude of the electron g factor is measured to be 0.4, and the rotation speed is 30 gigahertz in a 6.6 Tesla field. Geometric phases are detected in quantum dots for the first time due to cyclic Rabi oscillations driven by a resonant continuous-wave laser. These geometric phases provide another method of spin rotation and can be used in a gate. Any combination of these methods that provides spin rotation about two orthogonal axes can form an arbitrary rotation and together with a phase gate can form any unitary single qubit gate. Finally, this thesis also presents a detailed experimental procedure for creating a partial entanglement of internal variables within a quantum dot spin-exciton system, as a preliminary step to spin-photon entanglement. It has been proposed that entanglement between non-adjacent qubits in a large qubit network could occur via a photon, fueling research to demonstrate spin-photon entanglement. The experiment proposed here will create the precursor state in 25 picoseconds with a predicted fidelity of 0.985, and the precursor superposition state has a theoretical entropy of entanglement of 0.92.

•Jan 1, 2011•0 citations

Two-qubit conditional quantum-logic operation in a single self-assembled quantum dot

S. J. Boyle, A. J. Ramsay, Frank Bello +4 more

The four-level exciton/biexciton system of a single semiconductor quantum dot acts as a two-qubit register. We experimentally demonstrate an exciton-biexciton Rabi rotation conditional on the initial exciton spin in a single InGaAs/GaAs dot. This forms the basis of an optically gated two-qubit controlled rotation (CROT) quantum-logic operation where an arbitrary exciton spin is selected as the target qubit using the polarization of the control laser.

arXiv:0802.4368•Physical Review B•Aug 1, 2008•63 citations

Complete coherent control of spin qubits in self-assembled InAs quantum dots under oblique magnetic fields

I. Samaras, K. Barr, C. Schneider +2 more

We demonstrate complete coherent control of a single spin qubit confined in a self-assembled InAs negatively charged quantum dot subjected to an Oblique magnetic field, and directly compare this regime with the conventional Voigt geometry. In the Oblique-field configuration, the groundstate spin eigenstates are found to be unequal superpositions of the bare electron spin, with their composition tunable via the orientation of the applied field. This tunable spin mixing provides an additional degree of freedom to engineer the spin basis and associated optical couplings in the charged quantum dot system. Although this geometry has a distinct structure with important implications, it provides a regime in which we can fully and coherently control the tailored spin qubit. We observe Rabi oscillations and Ramsey fringes, and demonstrate arbitrary single-qubit rotations, enabling a direct comparison with the Voigt case. Our results establish that spin-qubit control does not necessarily require a pure Voigt geometry and can instead be achieved under Oblique magnetic fields. This relaxes constraints on device and field alignment and offers a versatile route to design and optimize quantum information processing architectures in semiconductor quantum dots.

quant-pharXiv:2604.07074•Apr 9, 2026

Two-Photon Coherent Polarization Flipping of Confined Excitons

Paweł Machnikowski

A two-photon process leading to coherent transitions between the two circularly polarized exciton states in a quantum dot is studied.It is shown that optical flipping of the exciton polarization is possible with picosecond laser pulses.The process is closely related to two-photon Rabi oscillations of a biexciton but it is much more stable against shifts of the laser frequency.

arXiv:0706.0858•Acta Physica Polonica A•Aug 1, 2007•1 citation

Coherent optical manipulation of a single spin state in a charged quantum dot: theory and modelling

Gabriela M. Slavcheva

The optically-induced coherent spin dynamics in a charged quantum dot (QD) is studied theoretically using a new dynamical model for rigorous description of circularly polarized ultrashort optical pulse resonant interactions with the electron-trion system. Generalized pseudospin master equation is derived for description of the time evolution of spin coherences and spin populations in terms of the real state pseudospin (coherence) vector including dissipation in the system through spin relaxation processes. The equation is solved in the time domain self-consistently with the vector Maxwell equations for the optical wave propagation coupled to it via macroscopic medium polarization. Using the model the long-lived electron spin coherence left behind a single resonant ultrashort optical excitation of the electron-trion transition in a charged QD is simulated in the lowand high-intensity Rabi oscillations regime. Signatures of the polarized photoluminescence (PL) resulting from the numerical simulations, such as the appearance of a second echo pulse after the excitation and a characteristic PL trace shape, specific for initial spin-up orientation, are discussed for realization of high-fidelity schemes for coherent readout of a single spin polarization state.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Sep 26, 2007•1 citation
Abstract We theoretically propose a scheme for the coherent manipulation of a single qubit, which is constructed using the self-trapped triplet exciton (STTE) in FM/polymer/FM sandwich. The STTE serves as a quantum dot, comprising two degenerate triplet states with opposite magnetizations, thereby forming the qubit’s subspace. We demonstrate that the spin state of this qubit can be coherently manipulated by applying an external circularly polarized laser (CPL) to form the Floquet state. The manipulation exhibits significant helicity dependence: when the CPL’s angular momentum is antiparallel to the STTE’s spin orientation, the STTE undergoes Rabi oscillations between the |↑↑〉 and |↓↓〉 state, corresponding to a π -rotation around the x -axis on the Bloch sphere. Conversely, when the CPL’s angular momentum is parallel to the STTE’s spin orientation, the STTE remains unresponsive to the CPL. Two-axis coherent control of the STTE qubit can be potentially realized by additionally applying a static magnetic field B z . Our work provides a theoretical perspective for realizing the coherent manipulation of a qubit in organic devices.
Introduction Quantum dots are often referred to as artificial atoms, since they trap carriers in discrete energy-levels due to the nanoscale three-dimensional finite potential energy well they provide. As such, dots exhibit a coherent light–matter interaction that is similar to an atom. This is evidenced by observations of atom–optics phenomena such as Rabi oscillations [43, 26], power broadening [27], Autler–Townes doublet [14, 42], Mollow triplet [42, 8], and coherent population trapping [6]. In this chapter, Rabi rotation measurements are used to examine how an exciton transition deviates from an ideal two-level atom due to its interaction with a reservoir of phonons. The neutral exciton transition may be regarded as a two-level system, or qubit, composed of the crystal ground-state ∣0〉 and a single electron-hole pair ∣ X 〉. The state-vector of a qubit can be described as a pseudo spin-half. When an oscillating electro-magnetic field resonantly excites the two-level transition it drives an oscillation in the population inversion known as a Rabi oscillation. This results from the oscillations of the driving field and the dipole of the two-level system being synchronous, such that in its rotating frame, the driving field acts as a static magnetic field that causes the pseudo-spin to rotate. Coherent control of the pseudo-spin can be achieved by applying well-defined driving fields, enabling the preparation, and manipulation of superposition states. Such coherent control concepts have found widespread use in electron spin, and nuclear magnetic resonance spectroscopy.
Optically driven self-assembled quantum dots are leading candidates for use in quantum computers because of their potential for high speed gate operations and relatively compact design. In this approach, each dot is charged with a single electron whose spin serves as the quantum bit (qubit). This thesis addresses the need for a universal set of gates to physically implement quantum computing and discusses initial steps toward spin-photon entanglement. Both are addressed through coherent control of the spin state in a magnetic field with optical pulses. This work experimentally demonstrates coherent rotations of the electron spin. First, the electron spin is rotated at up to 0.5 terahertz about the optical axis by a detuned picosecond optical pulse. The rotation occurs via a nearly resonant stimulated spin-flip Raman process involving a negatively charged exciton (trion). Second, rotation about an orthogonal axis is demonstrated due to electron spin precession about the magnetic field between two detuned optical pulses. The magnitude of the electron g factor is measured to be 0.4, and the rotation speed is 30 gigahertz in a 6.6 Tesla field. Geometric phases are detected in quantum dots for the first time due to cyclic Rabi oscillations driven by a resonant continuous-wave laser. These geometric phases provide another method of spin rotation and can be used in a gate. Any combination of these methods that provides spin rotation about two orthogonal axes can form an arbitrary rotation and together with a phase gate can form any unitary single qubit gate. Finally, this thesis also presents a detailed experimental procedure for creating a partial entanglement of internal variables within a quantum dot spin-exciton system, as a preliminary step to spin-photon entanglement. It has been proposed that entanglement between non-adjacent qubits in a large qubit network could occur via a photon, fueling research to demonstrate spin-photon entanglement. The experiment proposed here will create the precursor state in 25 picoseconds with a predicted fidelity of 0.985, and the precursor superposition state has a theoretical entropy of entanglement of 0.92.
We demonstrate complete coherent control of a single spin qubit confined in a self-assembled InAs negatively charged quantum dot subjected to an Oblique magnetic field, and directly compare this regime with the conventional Voigt geometry. In the Oblique-field configuration, the groundstate spin eigenstates are found to be unequal superpositions of the bare electron spin, with their composition tunable via the orientation of the applied field. This tunable spin mixing provides an additional degree of freedom to engineer the spin basis and associated optical couplings in the charged quantum dot system. Although this geometry has a distinct structure with important implications, it provides a regime in which we can fully and coherently control the tailored spin qubit. We observe Rabi oscillations and Ramsey fringes, and demonstrate arbitrary single-qubit rotations, enabling a direct comparison with the Voigt case. Our results establish that spin-qubit control does not necessarily require a pure Voigt geometry and can instead be achieved under Oblique magnetic fields. This relaxes constraints on device and field alignment and offers a versatile route to design and optimize quantum information processing architectures in semiconductor quantum dots.
The optically-induced coherent spin dynamics in a charged quantum dot (QD) is studied theoretically using a new dynamical model for rigorous description of circularly polarized ultrashort optical pulse resonant interactions with the electron-trion system. Generalized pseudospin master equation is derived for description of the time evolution of spin coherences and spin populations in terms of the real state pseudospin (coherence) vector including dissipation in the system through spin relaxation processes. The equation is solved in the time domain self-consistently with the vector Maxwell equations for the optical wave propagation coupled to it via macroscopic medium polarization. Using the model the long-lived electron spin coherence left behind a single resonant ultrashort optical excitation of the electron-trion transition in a charged QD is simulated in the lowand high-intensity Rabi oscillations regime. Signatures of the polarized photoluminescence (PL) resulting from the numerical simulations, such as the appearance of a second echo pulse after the excitation and a characteristic PL trace shape, specific for initial spin-up orientation, are discussed for realization of high-fidelity schemes for coherent readout of a single spin polarization state.