SciPost Submission Page
Flux-Tunable Hybridization in a Double Quantum Dot Interferometer
by Christian G. Prosko, Ivan Kulesh, Michael Chan, Lin Han, Di Xiao, Candice Thomas, Michael J. Manfra, Srijit Goswami, Filip K. Malinowski
Submission summary
| Authors (as registered SciPost users): | Christian Prosko |
| Submission information | |
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| Preprint Link: | scipost_202406_00018v1 (pdf) |
| Data repository: | https://zenodo.org/doi/10.5281/zenodo.7702118 |
| Date submitted: | 2024-06-10 20:33 |
| Submitted by: | Prosko, Christian |
| Submitted to: | SciPost Physics |
| Ontological classification | |
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| Academic field: | Physics |
| Specialties: |
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| Approach: | Experimental |
Abstract
Quantum interference of electron tunneling occurs in any system where multiple tunneling paths connect states. This unavoidably arises in two-dimensional semiconducting qubit arrays, and must be controlled as a prerequisite for the manipulation and readout of hybrid topological and parity qubits. Studying a loop formed by two quantum dots, we demonstrate a magnetic-flux-tunable hybridization between two electronic levels, an irreducibly simple system where quantum interference is expected to occur. Using radio-frequency reflectometry of the dots' gate electrodes we extract an interdot coupling exhibiting oscillations with a periodicity of one flux quantum. In different tunneling regimes we benchmark the oscillations' contrast, and find their amplitude varies with the charge state of the quantum dots. These results establish the feasibility and limitations of parity readout of qubits with tunnel couplings tuned by flux.
Author indications on fulfilling journal expectations
- Provide a novel and synergetic link between different research areas.
- Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
- Detail a groundbreaking theoretical/experimental/computational discovery
- Present a breakthrough on a previously-identified and long-standing research stumbling block
Current status:
Reports on this Submission
Strengths
1- Clear presentation of results and underlying physics
2- High quality data with clear interpretation
3- Demonstrating a proof-principle-measurement relevant for readout of topological qubits
Weaknesses
1- The system is relatively simple and behaves as expected.
Report
The authors present a quantum interference measurement of a circular double quantum dot probed via dispersive gate sensing. While there is a long history of measuring interferometers in mesoscopic devices, to my knowledge, this is the first demonstration of the interference in an isolated double quantum dot where readout needs to be performed by RF rather than transport measurements.
The overall setup is relatively simple (a ring-shaped double quantum dot with threaded flux). On one hand this allows for an excellent demonstration of an "irreducibly simple system where quantum interference is expected to occur", on the other hand the results are large exactly showing what one would expect out of such a simple system. What makes this paper more than only a pedagogical demonstration is the fact that the authors show that this simple system can actually be realized in a sizable mesoscopic device (micrometer long quantum dots) and that readout can be realized with dispersive gate sensing. Moreover, they explain some interesting subtleties in the level structure of the quantum dots. These findings are particularly relevant for the interferometric readout of topological qubits where similar quantum dot loops play a key role in many readout proposals.
Given this synergetic link and the clear path forward for more measurements in this direction I recommend the publication of the manuscript.
Requested changes
The timeliness of this paper is emphasized by the recently uploaded preprint arXiv:2401.09549 which uses similar measurements to read out the parity in an InAs-Al hybrid device. While the original arXiv posting of this manuscript clearly precedes this more recent preprint, I would assume that at the time of this review process a reference (or note) to this related preprint would be helpful for a reader.
Beyond that I have a few minor comments:
- Fig. 8: While it can be calculated given the bias, it would be useful to explicitly state the conductance values of the three regimes in 8b. How does open/intermediate/closed relate to e^2/h?
- App E: It is mentioned that $\tilde{\alpha}_i$ is different from the Coulomb blockade $\alpha_i$ due to the inter-dot capacitance. How important is that effect? What is the typical relative change of $\alpha$? Also, is it clear that an apparent difference is indeed due to the renormalization described in App F or could it also be due to uncertainty in the value of $L$ used to find $C_{\rm p}$?
- App E: It wasn't quite clear to me how $f_0$ is extracted in order to find $C_{\rm p}$. Do the authors perform a frequency sweep of the RF tone for each value of $V_L$, $V_R$ and $B_\perp$ in Fig 3 to determine $f_0$?
- App G: What are typical values of $\delta V_{\rm RF}$? Given that, how does the LZT condition compare to the measured values of $t_{\rm eff}$?
Recommendation
Publish (easily meets expectations and criteria for this Journal; among top 50%)