Chuyao Tong

All Publications

• Spin-valley locked excited states spectroscoy in a one-particle bilayer graphene quantum dot NATURE COMMUNICATIONS Duprez, H., Cances, S., Omahen, A., Masseroni, M., Ruckriegel, M. J., Adam, C., Tong, C., Garreis, R., Gerber, J. D., Huang, W., Gachter, L., Watanabe, K., Taniguchi, T., Ihn, T., Ensslin, K. 2024; 15 (1): 9717

  Abstract

  Current semiconductor qubits rely either on the spin or on the charge degree of freedom to encode quantum information. By contrast, in bilayer graphene the valley degree of freedom, stemming from the crystal lattice symmetry, is a robust quantum number that can therefore be harnessed for this purpose. The simplest implementation of a valley qubit would rely on two states with opposite valleys as in the case of a single-carrier bilayer graphene quantum dot immersed in a small perpendicular magnetic field (B⊥ ≲ 100 mT). However, the single-carrier quantum dot excited states spectrum has not been resolved to date in the relevant magnetic field range. Here, we fill this gap, by measuring the parallel and perpendicular magnetic field dependence of this spectrum with an unprecedented resolution of 4 μeV. We use a time-resolved charge detection technique that gives us access to individual tunnel events. Our results come as a direct verification of the predicted spectrum and establish a new upper-bound on inter-valley mixing, equal to our energy resolution. Our charge detection technique opens the door to measuring the relaxation time of a valley qubit in a single-carrier bilayer graphene quantum dot.

  View details for DOI 10.1038/s41467-024-54121-4

  View details for Web of Science ID 001352369200010

  View details for PubMedID 39521761

  View details for PubMedCentralID PMC11550441

• Spin-orbit proximity in MoS₂/bilayer graphene heterostructures NATURE COMMUNICATIONS Masseroni, M., Gull, M., Panigrahi, A., Jacobsen, N., Fischer, F., Tong, C., Gerber, J. D., Niese, M., Taniguchi, T., Watanabe, K., Levitov, L., Ihn, T., Ensslin, K., Duprez, H. 2024; 15 (1): 9251

  Abstract

  Van der Waals heterostructures provide a versatile platform for tailoring electronic properties through the integration of two-dimensional materials. Among these combinations, the interaction between bilayer graphene and transition metal dichalcogenides (TMDs) stands out due to its potential for inducing spin-orbit coupling (SOC) in graphene. Future devices concepts require the understanding of the precise nature of SOC in TMD/bilayer graphene heterostructures and its influence on electronic transport phenomena. Here, we experimentally confirm the presence of two distinct types of SOC - Ising (ΔI = 1.55 meV) and Rashba (ΔR = 2.5 meV) - in bilayer graphene when interfaced with molybdenum disulfide. Furthermore, we reveal a non-monotonic trend in conductivity with respect to the electric displacement field at charge neutrality. This phenomenon is ascribed to the existence of single-particle gaps induced by the Ising SOC, which can be closed by a critical displacement field. Our findings also unveil sharp peaks in the magnetoconductivity around the critical displacement field, challenging existing theoretical models.

  View details for DOI 10.1038/s41467-024-53324-z

  View details for Web of Science ID 001345548100015

  View details for PubMedID 39461982

  View details for PubMedCentralID PMC11513027

• Three-Carrier Spin Blockade and Coupling in Bilayer Graphene Double Quantum Dots PHYSICAL REVIEW LETTERS Tong, C., Ginzel, F., Kurzmann, A., Garreis, R., Ostertag, L., Gerber, J. D., Huang, W., Watanabe, K., Taniguchi, T., Burkard, G., Danon, J., Ihn, T., Ensslin, K. 2024; 133 (1): 017001

  Abstract

  The spin degrees of freedom is crucial for the understanding of any condensed matter system. Knowledge of spin-mixing mechanisms is not only essential for successful control and manipulation of spin qubits, but also uncovers fundamental properties of investigated devices and material. For electrostatically defined bilayer graphene quantum dots, in which recent studies report spin-relaxation times T_{1} up to 50 ms with strong magnetic field dependence, we study spin-blockade phenomena at charge configuration (1,2)↔(0,3). We examine the dependence of the spin-blockade leakage current on interdot tunnel coupling and on the magnitude and orientation of externally applied magnetic field. In out-of-plane magnetic field, the observed zero-field current peak could arise from finite-temperature cotunneling with the leads; though involvement of additional spin- and valley-mixing mechanisms are necessary for explaining the persistent sharp side peaks observed. In in-plane magnetic field, we observe a zero-field current dip, attributed to the competition between the spin Zeeman effect and the Kane-Mele spin-orbit interaction. Details of the line shape of this current dip, however, suggest additional underlying mechanisms are at play.

  View details for DOI 10.1103/PhysRevLett.133.017001

  View details for Web of Science ID 001262611100008

  View details for PubMedID 39042804

• Electric Dipole Coupling of a Bilayer Graphene Quantum Dot to a High-Impedance Microwave Resonator NANO LETTERS Ruckriegel, M. J., Gachter, L. M., Kealhofer, D., Panah, M., Tong, C., Adam, C., Masseroni, M., Duprez, H., Garreis, R., Watanabe, K., Taniguchi, T., Wallraff, A., Ihn, T., Ensslin, K., Huang, W. 2024

  Abstract

  We implement circuit quantum electrodynamics (cQED) with quantum dots in bilayer graphene, a maturing material platform that can host long-lived spin and valley states. Our device combines a high-impedance (Zr ≈ 1 kΩ) superconducting microwave resonator with a double quantum dot electrostatically defined in a graphene-based van der Waals heterostructure. Electric dipole coupling between the subsystems allows the resonator to sense the electric susceptibility of the double quantum dot from which we reconstruct its charge stability diagram. We achieve sensitive and fast detection of the interdot transition with a signal-to-noise ratio of 3.5 within 1 μs integration time. The charge-photon interaction is quantified in the dispersive and resonant regimes by comparing the resonator response to input-output theory, yielding a coupling strength of g/2π = 49.7 MHz. Our results introduce cQED as a probe for quantum dots in van der Waals materials and indicate a path toward coherent charge-photon coupling with bilayer graphene quantum dots.

  View details for DOI 10.1021/acs.nanolett.4c01791

  View details for Web of Science ID 001239435500001

  View details for PubMedID 38833415

• Long distance electron-electron scattering detected with point contacts PHYSICAL REVIEW RESEARCH Ginzburg, L. V., Wu, Y., Roeoesli, M. P., Gomez, P., Garreis, R., Tong, C., Stara, V., Gold, C., Nazaryan, K., Kryhin, S., Overweg, H., Reichl, C., Berl, M., Taniguchi, T., Watanabe, K., Wegscheider, W., Ihn, T., Ensslin, K. 2023; 5 (4)

  View details for DOI 10.1103/PhysRevResearch.5.043088

  View details for Web of Science ID 001258123600002