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Ultra-Slow Orbital and Spin Dynamics in an Electrically Tunable Quantum Dot Molecule

Christopher Thalacker1,*, Michelle Lienhart1, Markus Stöcker1, Nadeem Akhlaq1, Irina Ivanova1, Nikolai Bart2, Arne Ludwig2, Johannes Schall3, Stephan Reitzenstein3 et al.

Dirk Reuter4, Steffen Wilksen5, Christopher Gies5, Krzysztof Gawarecki6, Paweł Machnikowski6, Kai Müller7, and Jonathan Finley1

  • *Contact author: christopher.thalacker@tum.de
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PRX Quantum 7, 033056 – Published 14 September, 2026

DOI: https://doi.org/10.1103/qgr2-968q

Abstract

Tunnel-coupled optically active quantum dot molecules (QDMs) have the potential to operate as spin-photon interfaces with coupled spins that interact with two different photon frequencies at the same time. A prerequisite is to deterministically prepare two (electron or hole) spins in the QDM and be able to electrically tune the orbital state couplings. Here, we demonstrate the sequential optical charging of a single QDM with two-electron spins while simultaneously maintaining the ability to widely tune orbital couplings using static electric fields and optically drive the system for quantum light generation. We optically prepare one- and two-spin states, initialize via optical pumping and explore orbital and spin relaxation dynamics for one- and two-spin states as a function of the energy detuning and hybridization of orbital states. For two-spin states, remarkably long singlet-triplet relaxation times are observed, extending beyond ∼100  μs with strong dependence on the relative energy of ground and excited two-spin states. Qualitative agreement is observed with k·p calculations of phonon-mediated spin relaxation. Our results provide new quantitative understanding of the dynamics of one- and two-spin states and address a number of key prerequisites for using QDMs to create multidimensional photonic cluster states.

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Popular Summary

Quantum technologies from quantum computers to quantum networks rely on the ability to store and manipulate quantum information for as long as possible. Semiconductor quantum dots are promising building blocks for such technologies: they can trap individual electrons whose quantum state, or “spin,” carries information, and they can interact with light, making them ideal bridges between stationary and flying qubits. In this work, we study a more complex version of a single quantum dot: a quantum dot molecule, formed by two coupled quantum dots stacked on top of each other. We show that this system can be loaded with two individual electron spins using light alone, while simultaneously allowing the coupling between the two dots to be tuned electrically. This combination of optical spin control and electrical tunability is a key step toward using such systems as interfaces between spin-based quantum memories and photonic quantum networks. Most strikingly, we find that the two-spin system can maintain its quantum state for remarkably long times exceeding 100 ms. This is an unusually long spin lifetime for this class of devices and arises from a subtle interplay between the orbital and spin degrees of freedom of the system. These findings bring semiconductor quantum dot molecules closer to being practical, electrically controllable nodes in future quantum networks.

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References (63)

  1. D. D. Awschalom, R. Hanson, J. Wrachtrup, and B. B. Zhou, Quantum technologies with optically interfaced solid-state spins, Nat. Photonics 12, 516 (2018).
  2. L. Hanschke, K. A. Fischer, S. Appel, D. Lukin, J. Wierzbowski, S. Sun, R. Trivedi, J. Vučković, J. J. Finley, and K. Müller, Quantum dot single-photon sources with ultra-low multi-photon probability, npj Quantum Inf. 4, 43 (2018).
  3. S. Thomas, M. Billard, N. Coste, S. Wein, H. Ollivier, O. Krebs, L. Tazaïrt, A. Harouri, A. Lemaitre, I. Sagnes, C. Anton, L. Lanco, N. Somaschi, J. Loredo, and P. Senellart, Bright polarized single-photon source based on a linear dipole, Phys. Rev. Lett. 126, 233601 (2021).
  4. N. Akopian, N. H. Lindner, E. Poem, Y. Berlatzky, J. Avron, D. Gershoni, B. D. Gerardot, and P. M. Petroff, Entangled photon pairs from semiconductor quantum dots, Phys. Rev. Lett. 96, 130501 (2006).
  5. D. Press, T. D. Ladd, B. Zhang, and Y. Yamamoto, Complete quantum control of a single quantum dot spin using ultrafast optical pulses, Nature (London) 456, 218 (2008).
  6. W. B. Gao, P. Fallahi, E. Togan, J. Miguel-Sanchez, and A. Imamoglu, Observation of entanglement between a quantum dot spin and a single photon, Nature (London) 491, 426 (2012).
  7. R. Stockill, M. Stanley, L. Huthmacher, E. Clarke, M. J. Hugues, A. J. Miller, C. Matthiesen, C. Le Gall, and M. Atatüre, Phase-tuned entangled state generation between distant spin qubits, Phys. Rev. Lett. 119, 010503 (2017).
  8. N. H. Lindner and T. Rudolph, Proposal for pulsed on-demand sources of photonic cluster state strings, Phys. Rev. Lett. 103, 113602 (2009).
  9. I. Schwartz, E. Schmidgall, L. Gantz, D. Cogan, E. Bordo, Y. Don, M. Zielinski, and D. Gershoni, Determinisitic writing and control of the dark exciton spin using short single optical pulses, Phys. Rev. X 5, 011009 (2015).
  10. D. Cogan, Z.-E. Su, O. Kenneth, and D. Gershoni, Deterministic generation of indistinguishable photons in a cluster state, Nat. Photonics 17, 324 (2023).
  11. N. Coste, D. A. Fioretto, N. Belabas, S. C. Wein, P. Hilaire, R. Frantzeskakis, M. Gundin, B. Goes, N. Somaschi, M. Morassi, A. Lemaître, I. Sagnes, A. Harouri, S. E. Economou, A. Auffeves, O. Krebs, L. Lanco, and P. Senellart, High-rate entanglement between a semiconductor spin and indistinguishable photons, Nat. Photonics 17, 582 (2023).
  12. R. Raussendorf, D. E. Browne, and H. J. Briegel, Measurement-based quantum computation on cluster states, Phys. Rev. A 68, 022312 (2003).
  13. D. E. Browne and T. Rudolph, Resource-efficient linear optical quantum computation, Phys. Rev. Lett. 95, 010501 (2005).
  14. S. E. Economou, N. Lindner, and T. Rudolph, Optically generated 2-dimensional photonic cluster state from coupled quantum dots, Phys. Rev. Lett. 105, 093601 (2010).
  15. M. Gimeno-Segovia, T. Rudolph, and S. E. Economou, Deterministic generation of large-scale entangled photonic cluster state from interacting solid state emitters, Phys. Rev. Lett. 123, 070501 (2019).
  16. H. J. Krenner, M. Sabathil, E. C. Clark, A. Kress, D. Schuh, M. Bichler, G. Abstreiter, and J. J. Finley, Direct observation of controlled coupling in an individual quantum dot molecule, Phys. Rev. Lett. 94, 057402 (2005).
  17. M. F. Doty, M. Scheibner, A. S. Bracker, I. V. Ponomarev, T. L. Reinecke, and D. Gammon, Optical spectra of doubly charged quantum dot molecules in electric and magnetic fields, Phys. Rev. B 78, 115316 (2008).
  18. H. Bluhm, S. Foletti, I. Neder, M. Rudner, D. Mahalu, V. Umansky, and A. Yacoby, Dephasing time of GaAs electron-spin qubits coupled to a nuclear bath exceeding 200  μs, Nat. Phys. 7, 109 (2011).
  19. K. M. Weiss, J. M. Elzerman, Y. L. Delley, J. Miguel-Sanchez, and A. Imamoğlu, Coherent two-electron spin qubits in an optically active pair of coupled InGaAs quantum dots, Phys. Rev. Lett. 109, 107401 (2012).
  20. K. X. Tran, A. S. Bracker, M. K. Yakes, J. Q. Grim, and S. G. Carter, Enhanced spin coherence of a self-assembled quantum dot molecule at the optimal electrical bias, Phys. Rev. Lett. 129, 027403 (2022).
  21. Y. L. Delley, M. Kroner, S. Faelt, W. Wegscheider, and A. İmamoğlu, Deterministic entanglement between a propagating photon and a singlet-triplet qubit in an optically active quantum dot molecule, Phys. Rev. B 96, 241410 (2017).
  22. S. E. Economou and T. L. Reinecke, Optically induced spin gates in coupled quantum dots using the electron-hole exchange interaction, Phys. Rev. B 78, 115306 (2008).
  23. D. Kim, S. G. Carter, A. Greilich, A. S. Bracker, and D. Gammon, Ultrafast optical control of entanglement between two quantum-dot spins, Nat. Phys. 7, 223 (2011).
  24. A. Greilich, S. G. Carter, D. Kim, A. S. Bracker, and D. Gammon, Optical control of one and two hole spins in interacting quantum dots, Nat. Photonics 5, 702 (2011).
  25. F. Bopp, J. Rojas, N. Revenga, H. Riedl, F. Sbresny, K. Boos, T. Simmet, A. Ahmadi, D. Gershoni, J. Kasprzak, A. Ludwig, S. Reitzenstein, A. Wieck, D. Reuter, K. Müller, and J. J. Finley, Quantum dot molecule devices with optical control of charge status and electronic control of coupling, Adv. Quantum Technol. 5, 2200049 (2022).
  26. F. Bopp, J. Schall, N. Bart, F. Vögl, C. Cullip, F. Sbresny, K. Boos, C. Thalacker, M. Lienhart, S. Rodt, D. Reuter, A. Ludwig, A. D. Wieck, S. Reitzenstein, K. Müller, and J. J. Finley, Coherent driving of direct and indirect excitons in a quantum dot molecule, Phys. Rev. B 107, 165426 (2023).
  27. I. Schwartz, D. Cogan, E. R. Schmidgall, Y. Don, L. Gantz, O. Kenneth, N. H. Lindner, and D. Gershoni, Deterministic generation of a cluster state of entangled photons, Science 354, 434 (2016). 
  28. S. Rodt and S. Reitzenstein, High-performance deterministic in situ electron-beam lithography enabled by cathodoluminescence spectroscopy, Nano Express 2, 014007 (2021).
  29. J. Schall, M. Deconinck, N. Bart, M. Florian, M. von Helversen, C. Dangel, R. Schmidt, L. Bremer, F. Bopp, I. Hüllen, C. Gies, D. Reuter, A. D. Wieck, S. Rodt, J. J. Finley, F. Jahnke, A. Ludwig, and S. Reitzenstein, Bright electrically controllable quantum-dot-molecule devices fabricated by in situ electron-beam lithography, Adv. Quantum Technol. 4, 2100002 (2021).
  30. M. Bayer, P. Hawrylak, K. Hinzer, S. Fafard, M. Korkusinski, Z. R. Wasilewski, O. Stern, and A. Forchel, Coupling and entangling of quantum states in quantum dot molecules, Science 291, 451 (2001).
  31. R. J. Warburton, Single spins in self-assembled quantum dots, Nat. Mater. 12, 483 (2013).
  32. A. Bechtold, D. Rauch, F. Li, T. Simmet, P.-L. Ardelt, A. Regler, K. Müller, N. A. Sinitsyn, and J. J. Finley, Three-stage decoherence dynamics of an electron spin qubit in an optically active quantum dot, Nat. Phys. 11, 1005 (2015).
  33. J. R. Petta, A. C. Johnson, J. M. Taylor, E. A. Laird, A. Yacoby, M. D. Lukin, C. M. Marcus, M. P. Hanson, and A. C. Gossard, Coherent manipulation of coupled electron spins in semiconductor quantum dots, Science 309, 2180 (2005).
  34. M. C. Löbl, C. Spinnler, A. Javadi, L. Zhai, G. N. Nguyen, J. Ritzmann, L. Midolo, P. Lodahl, A. D. Wieck, A. Ludwig, and R. J. Warburton, Radiative Auger process in the single-photon limit, Nature Nanotechnol. 15, 558 (2020).
  35. A. Kurzmann, A. Ludwig, A. D. Wieck, A. Lorke, and M. Geller, Auger recombination in self-assembled quantum dots: quenching and broadening of the charged exciton transition, Nano Lett. 16, 3367 (2016).
  36. S. Wilksen, F. Lohof, I. Willmann, F. Bopp, M. Lienhart, C. Thalacker, J. Finley, M. Florian, and C. Gies, Gate-based protocol simulations for quantum repeaters using quantum-dot molecules in switchable electric fields, Adv. Quantum Technol. 7, 2300280 (2024).
  37. M. Born and V. Fock, Beweis des adiabatensatzes, Zeitschrift für Physik 51, 165 (1928).
  38. T. Kato, On the adiabatic theorem of quantum mechanics, J. Phys. Soc. Jpn. 5, 435 (1950).
  39. K. Müller, A. Bechtold, C. Ruppert, M. Zecherle, G. Reithmaier, M. Bichler, H. J. Krenner, G. Abstreiter, A. W. Holleitner, J. M. Villas-Boas, M. Betz, and J. J. Finley, Electrical control of inter-dot electron tunneling in a quantum dot molecule, Phys. Rev. Lett. 108, 197402 (2012).
  40. K. Gawarecki and P. Machnikowski, Phonon-assisted relaxation between triplet and singlet states in a self-assembled double quantum dot, Sci. Rep. 11, 15256 (2021).
  41. A. V. Khaetskii and Y. V. Nazarov, Spin relaxation in semiconductor quantum dots, Phys. Rev. B 61, 12639 (2000).
  42. A. V. Khaetskii and Y. V. Nazarov, Spin-flip transitions between Zeeman sublevels in semiconductor quantum dots, Phys. Rev. B 64, 125316 (2001).
  43. K. Gawarecki, Spin-orbit coupling and magnetic-field dependence of carrier states in a self-assembled quantum dot, Phys. Rev. B 97, 235408 (2018).
  44. M. Lienhart, K. Gawarecki, M. Stöcker, F. Bopp, C. Cullip, N. Akhlaq, C. Thalacker, J. Schall, S. Rodt, A. Ludwig, D. Reuter, S. Reitzenstein, K. Müller, P. Machnikowski, and J. J. Finley, Resonant and antiresonant exciton-phonon coupling in quantum dot molecules, Phys. Rev. B 112, 235305 (2025).
  45. B. Urbaszek, X. Marie, T. Amand, O. Krebs, P. Voisin, P. Maletinsky, A. Högele, and A. Imamoglu, Nuclear spin physics in quantum dots: An optical investigation, Rev. Mod. Phys. 85, 79 (2013).
  46. P. Y. Yu and M. Cardona, Fundamentals of Semiconductors, 3rd ed. (Springer, Berlin, 2005).
  47. A. Grodecka, L. Jacak, P. Machnikowski, and K. Roszak, Phonon impact on the coherent control of quantum states in semiconductor quantum dots, in Quantum Dots: Research Developments, edited by P. A. Ling (Nova Science, NY, 2005), pp. 47–88, cond-mat/0404364.
  48. M. Krzykowski, K. Gawarecki, and P. Machnikowski, Hole spin-flip transitions in a self-assembled quantum dot, Phys. Rev. B 102, 205301 (2020).
  49. P. Karwat, K. Gawarecki, and P. Machnikowski, Hole spin-flip transitions in a self-assembled quantum dot, Phys. Rev. B 104, 045308 (2021).
  50. S. Wijitpatima, N. Auler, P. Mudi, T. Funk, A. Barua, B. Shrestha, J. Schall, I. Limame, S. Rodt, D. Reuter, and S. Reitzenstein, Bright electrically contacted circular Bragg grating resonators with deterministically integrated quantum dots, ACS Nano 18, 31834 (2024).
  51. M. Scheibner, M. F. Doty, I. V. Ponomarev, A. S. Bracker, E. A. Stinaff, V. L. Korenev, T. L. Reinecke, and D. Gammon, Spin fine structure of optically excited quantum dot molecules, Phys. Rev. B 75, 245318 (2007).
  52. M. Bayer, G. Ortner, O. Stern, A. Kuther, A. A. Gorbunov, A. Forchel, P. Hawrylak, S. Fafard, K. Hinzer, T. L. Reinecke, S. N. Walck, J. P. Reithmaier, F. Klopf, and F. Schäfer, Fine structure of neutral and charged excitons in self-assembled In(Ga)As/(Al)GaAs quantum dots, Phys. Rev. B 65, 195315 (2002).
  53. H. Haug and A.-P. Jauho, Quantum Kinetics in Transport and Optics of Semiconductors (Springer, New York, 2008).
  54. W. W. Chow and F. Jahnke, On the physics of semiconductor quantum dots for applications in lasers and quantum optics, Prog. Quantum Electron. 37, 109 (2013).
  55. O. Gywat, H. J. Krenner, and J. Berezovsky, Spins in Optically Active Quantum Dots: Concepts and Methods (John Wiley & Sons, New York, 2010).
  56. M. Gawełczyk and K. Gawarecki, Tunneling-related electron spin relaxation in self-assembled quantum-dot molecules, Phys. Rev. B 103, 245422 (2021).
  57. D. Farfurnik, R. M. Pettit, Z. Luo, and E. Waks, Single-shot readout of a solid-state spin in a decoherence-free subspace, Phys. Rev. Appl. 15, L031002 (2021).
  58. V. Jovanov, T. Eissfeller, S. Kapfinger, E. C. Clark, F. Klotz, M. Bichler, J. G. Keizer, P. M. Koenraad, M. S. Brandt, G. Abstreiter, and J. J. Finley, Highly nonlinear excitonic Zeeman spin splitting in composition-engineered artificial atoms, Phys. Rev. B 85, 165433 (2012).
  59. M. A. Migliorato, A. G. Cullis, M. Fearn, and J. H. Jefferson, Atomistic simulation of strain relaxation in InxGa1−xAs/GaAs quantum dots with nonuniform composition, Phys. Rev. B 65, 115316 (2002).
  60. C. Pryor, J. Kim, L. W. Wang, A. J. Williamson, and A. Zunger, Comparison of two methods for describing the strain profiles in quantum dots, J. Appl. Phys. 83, 2548 (1998).
  61. I. Vurgaftman, J. R. Meyer, and L. R. Ram-Mohan, Band parameters for III–V compound semiconductors and their alloys, J. Appl. Phys. 89, 5815 (2001).
  62. G. Bester, X. Wu, D. Vanderbilt, and A. Zunger, Importance of second-order piezoelectric effects in zinc-blende semiconductors, Phys. Rev. Lett. 96, 187602 (2006).
  63. M. A. Caro, S. Schulz, and E. P. O’Reilly, Origin of nonlinear piezoelectricity in III-V semiconductors: Internal strain and bond ionicity from hybrid-functional density functional theory, Phys. Rev. B 91, 75203 (2015).

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PRX Quantum 7, 033056– Published 14 September, 2026
  • Received 9 March 2026
  • Accepted 10 August 2026
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