Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Optical initialization of a single spin-valley in charged WSe2 quantum dots


Control and manipulation of single charges and their internal degrees of freedom, such as spin, may enable applications in quantum information technology, spintronics and quantum sensing1,2. Recently, atomically thin semiconductors with a direct bandgap such as group VI-B transition-metal dichalcogenide monolayers have emerged as a platform for valleytronics—the study of the valley degree of freedom of charge carriers to store and control information. They offer optical, magnetic and electrical control of the valley index, which, with the spin, is locked into a robust spin-valley index3,4. However, because recombination lifetimes of photogenerated excitations in transition-metal dichalcogenides are of the order of a few picoseconds, optically generated valley excitons possess similar lifetimes. On the other hand, the valley polarization of free holes has a lifetime of microseconds5,6,7,8,9. Whereas progress has been made in optical control of the valley index in ensembles of charge carriers10,11,12, valley control of individual charges, which is crucial for valleytronics, remains unexplored. Here we provide unambiguous evidence for localized holes with a net spin in optically active WSe2 quantum dots13,14,15,16,17 and we initialize their spin-valley state with the helicity of the excitation laser under small magnetic fields. Under such conditions, we estimate a lower bound of the valley lifetime of a single charge in a quantum dot from the recombination time to be of the order of nanoseconds. Remarkably, neutral quantum dots do not exhibit such spin-valley initialization, which illustrates the role of the excess charge in prolonging the valley lifetime. Our work extends the field of two-dimensional valleytronics to the level of single spin- valleys, with implications for quantum information and sensing applications.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Singly charged QDs and charge control in a monolayer WSe2 field effect transistor.
Fig. 2: Charged and neutral QDs in monolayer WSe2.
Fig. 3: Zeeman splitting and circular polarization of positively charged QDs in monolayer WSe2.
Fig. 4: Optical initialization of a positively charged QD under magnetic field.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


  1. 1.

    Imamoğlu, A. et al. Quantum information processing using quantum dot spins and cavity-QED. Phys. Rev. Lett. 83, 4204–4207 (1999).

    Article  Google Scholar 

  2. 2.

    Giovannetti, V., Lloyd, S. & Maccone, L. Advances in quantum metrology. Nat. Photon. 5, 222–229 (2011).

    CAS  Article  Google Scholar 

  3. 3.

    Xiao, D., Liu, G.-B., Feng, W., Xu, X. & Yao, W. Coupled spin and valley physics in monolayers of MoS2 and other group-VI dichalcogenides. Phys. Rev. Lett. 108, 196802 (2012).

    Article  Google Scholar 

  4. 4.

    Xu, X., Yao, W., Xiao, D. & Heinz, T. F. Spin and pseudospins in layered transition metal dichalcogenides. Nat. Phys. 10, 343–350 (2014).

    CAS  Article  Google Scholar 

  5. 5.

    Jiang, C. et al. Microsecond dark-exciton valley polarisation memory in two-dimensional heterostructures. Nat. Commun. 9, 753 (2018).

    Article  Google Scholar 

  6. 6.

    Yang, L. et al. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2. Nat. Phys. 11, 830–834 (2015).

    CAS  Article  Google Scholar 

  7. 7.

    Dey, P. et al. Gate-controlled spin-valley locking of resident carriers in WSe2 monolayers. Phys. Rev. Lett. 119, 137401 (2017).

    CAS  Article  Google Scholar 

  8. 8.

    Kim, J. et al. Observation of ultralong valley lifetime in WSe2/MoS2 heterostructures. Sci. Adv. 3, e1700518 (2017).

    Article  Google Scholar 

  9. 9.

    Yan, T., Yang, S., Li, D. & Cui, X. Long valley relaxation time of free carriers in monolayer WSe2. Phys. Rev. B 95, 241406 (2017).

    Article  Google Scholar 

  10. 10.

    Mak, K. F., He, K., Shan, J. & Heinz, T. F. Control of valley polarisation in monolayer MoS2 by optical helicity. Nat. Nanotechnol. 7, 494–498 (2012).

    CAS  Article  Google Scholar 

  11. 11.

    Zeng, H., Dai, J., Yao, W., Xiao, D. & Cui, X. Valley polarisation in MoS2 monolayers by optical pumping. Nat. Nanotechnol. 7, 490–493 (2012).

    CAS  Article  Google Scholar 

  12. 12.

    Cao, T. et al. Valley-selective circular dichroism of monolayer molybdenum disulphide. Nat. Commun. 3, 887 (2012).

    Article  Google Scholar 

  13. 13.

    Srivastava, A. et al. Optically active quantum dots in monolayer WSe2. Nat. Nanotechnol. 10, 491–496 (2015).

    CAS  Article  Google Scholar 

  14. 14.

    Koperski, M. et al. Single photon emitters in exfoliated WSe2 structures. Nat. Nanotechnol. 10, 503–506 (2015).

    CAS  Article  Google Scholar 

  15. 15.

    Chakraborty, C., Kinnischtzke, L., Goodfellow, K. M., Beams, R. & Vamivakas, A. N. Voltage-controlled quantum light from an atomically thin semiconductor. Nat. Nanotechnol. 10, 507–511 (2015).

    CAS  Article  Google Scholar 

  16. 16.

    He, Y.-M. et al. Single quantum emitters in monolayer semiconductors. Nat. Nanotechnol. 10, 497–502 (2015).

    CAS  Article  Google Scholar 

  17. 17.

    Tonndorf, P. et al. Single-photon emission from localised excitons in an atomically thin semiconductor. Optica 2, 347–352 (2015).

    CAS  Article  Google Scholar 

  18. 18.

    Branny, A., Kumar, S., Proux, R. & Gerardot, B. D. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor. Nat. Commun. 8, 15053 (2017).

    CAS  Article  Google Scholar 

  19. 19.

    Palacios-Berraquero, C. et al. Large-scale quantum-emitter arrays in atomically thin semiconductors. Nat. Commun. 8, 15093 (2017).

    CAS  Article  Google Scholar 

  20. 20.

    Schwarz, S. et al. Electrically pumped single-defect light emitters in WSe2. 2D Mater. 3, 025038 (2016).

    Article  Google Scholar 

  21. 21.

    Srivastava, A. et al. Valley Zeeman effect in elementary optical excitations of monolayer WSe2. Nat. Phys. 11, 141–147 (2015).

    CAS  Article  Google Scholar 

  22. 22.

    Stier, A. V., McCreary, K. M., Jonker, B. T., Kono, J. & Crooker, S. A. Exciton diamagnetic shifts and valley Zeeman effects in monolayer WS2 and MoS2 to 65 tesla. Nat. Commun. 7, 10643 (2016).

    CAS  Article  Google Scholar 

  23. 23.

    Yu, H., Liu, G.-B., Gong, P., Xu, X. & Yao, W. Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides. Nat. Commun. 5, 3876 (2014).

    CAS  Article  Google Scholar 

  24. 24.

    Courtade, E. et al. Charged excitons in monolayer WSe2: experiment and theory. Phys. Rev. B 96, 085302 (2017).

    Article  Google Scholar 

  25. 25.

    Högele, A. et al. Voltage-controlled optics of a quantum dot. Phys. Rev. Lett. 93, 217401 (2004).

    Article  Google Scholar 

  26. 26.

    Chakraborty, C. et al. 3D localised trions in monolayer WSe2 in a charge tuneable van der Waals heterostructure. Nano Lett. 18, 2859–2863 (2018).

    CAS  Article  Google Scholar 

  27. 27.

    Regelman, D. V. et al. Optical spectroscopy of single quantum dots at tuneable positive, neutral, and negative charge states. Phys. Rev. B 64, 165301 (2001).

    Article  Google Scholar 

  28. 28.

    Aivazian, G. et al. Magnetic control of valley pseudospin in monolayer WSe2. Nat. Phys. 11, 148–152 (2015).

    CAS  Article  Google Scholar 

  29. 29.

    MacNeill, D. et al. Breaking of valley degeneracy by magnetic field in monolayer MoSe2. Phys. Rev. Lett. 114, 037401 (2015).

    Article  Google Scholar 

  30. 30.

    Li, Y. et al. Valley splitting and polarisation by the Zeeman effect in monolayer MoSe2. Phys. Rev. Lett. 113, 266804 (2014).

    Article  Google Scholar 

  31. 31.

    Wu, Y., Tong, Q., Liu, G.-B., Yu, H. & Yao, W. Spin-valley qubit in nanostructures of monolayer semiconductors: optical control and hyperfine interaction. Phys. Rev. B 93, 045313 (2016).

    Article  Google Scholar 

  32. 32.

    Sharma, G., Economou, S. E. & Barnes, E. Interplay of valley polarisation and dynamic nuclear polarisation in 2D transition metal dichalcogenides. Phys. Rev. B 96, 125201 (2017).

    Article  Google Scholar 

  33. 33.

    Atatüre, M., Dreiser, J., Badolato, A. & Imamoğlu, A. Observation of Faraday rotation from a single confined spin. Nat. Phys. 3, 101–106 (2007).

    Article  Google Scholar 

Download references


We thank A. Imamoğlu and M. Kroner for many discussions. We also acknowledge technical help from T. Neal and E. Liu. A.S. acknowledges support from Emory University startup funds and the NSF through the EFRI programme (grant number EFMA-1741691). Q.X. gratefully acknowledges strong support from Singapore National Research Foundation via an NRF-ANR joint grant (numbef NRF2017-NRF-ANR002 2D-Chiral) and the Singapore Ministry of Education via an AcRF Tier2 grant (number MOE2017-T2-1-040) and Tier1 grants (RG 113/16 and RG 194/17).

Author information




X.L. and A.S. conceived and designed the experiments. X.L., X.C., S.D., Q.Y. and W.L. performed the experiments. X.L. and X.W. prepared the samples. X.L., X.C., S.D., Q.X. and A.S. analysed the data. Q.X. contributed materials. X.L. and A.S. co-wrote the paper.

Corresponding authors

Correspondence to Xin Lu or Ajit Srivastava.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Journal peer review information: Nature Nanotechnology thanks Ziliang Ye and other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figures 1–16, Supplementary Tables 1,2

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Lu, X., Chen, X., Dubey, S. et al. Optical initialization of a single spin-valley in charged WSe2 quantum dots. Nat. Nanotechnol. 14, 426–431 (2019).

Download citation

Further reading


Quick links

Find nanotechnology articles, nanomaterial data and patents all in one place. Visit Nano by Nature Research