SciPost Submission Page
Theory of Andreev Blockade in a Double Quantum Dot with a Superconducting Lead
by David Pekker, Po Zhang, Sergey M. Frolov
|As Contributors:||Sergey Frolov|
|Arxiv Link:||https://arxiv.org/abs/1810.05112v2 (pdf)|
|Date submitted:||2021-08-25 15:48|
|Submitted by:||Frolov, Sergey|
|Submitted to:||SciPost Physics|
A normal metal source reservoir can load two electrons onto a double quantum dot in the spin-triplet configuration. We show that if the drain lead of the dot is a spin-singlet superconductor, these electrons cannot form a Cooper pair and are blockaded on the double dot. We call this phenomenon Andreev blockade because it arises due to suppressed Andreev reflections. We identify transport characteristics unique to Andreev blockade. Most significantly, it occurs for any occupation of the dot adjacent to the superconductor, in contrast with the well-studied Pauli blockade which requires odd occupations. Andreev blockade is lifted if quasiparticles are allowed to enter the superconducting lead, but it should be observable in the hard gap superconductor-semiconductor devices. A recent experiment tests this model and finds support for several predictions made here~[P. Zhang, H. Wu, J. Chen, S. A. Khan, P. Krogstrup, D. Pekker, and S. M. Frolov, arXiv:2102.03283 (2021)]. Andreev blockade should be considered in the design of topological quantum circuits, hybrid quantum bits and quantum emulators.
For Journal SciPost Physics: Publish
(status: Editorial decision fixed and (if required) accepted by authors)
Submission & Refereeing History
You are currently on this page
Reports on this Submission
Anonymous Report 2 on 2021-9-24 (Invited Report)
1. clear presentation of the transport phenomenon in question
2. immediate experimental relevance
3. several interesting detailed predictions
1. While it is a paper on theory, there is virtually no theoretical analysis (see the report)
2. Minor shortcomings in presentation/reasoning.
3. Similar transport phenomena have been studied\discussed in the literature.
Let me immediately report that the paper does not satisfy the acceptance criteria of SciPost. This is not because the paper is bad: it is rather about the criteria. To require from a good paper to report on "groundbreaking results" is either hypocrisy or madness. If it were realistic, in short time we would not have any ground to break. Anyway, I was asked to check the criteria, and this paper does not fit those. Perhaps SciPostPhysCore is a better destination.
This paper clarifies a transport phenomenon and gives name to it. Owing to the conceptual simplicity of the effect, similar transport features have been discussed in the literature the authors cite. Yet nobody has presented it with such concentation and detail. In contrast to the opinion of another referee, I do not think the Ref 26 did so.
Although the paper is on theory, the quantitative theoretical analysis is virtually absent: there are only 2 formulas in the paper representing the Hamiltonian, and many qualitative statements. All of them are relevant, and perhaps the simplicity of the effect makes the theoretical analysis rather redundant.
I've found 3 statements of secondary importance that do not sound good to me, perhaps because of the formulation. I would suggest the authors either correct or explain in more detail.
1. "The origin of Andreev blockade is angular momentum conservation:" There is no angular momentum conservation in the setup since the potential experienced by electrons is rather far from being spherically symmetric. The authors might mean spin conservation.
2. "While Andreev blockade happens at the dot-lead interface" I do not understand the use of "interface" here. Is there a statement about a physical location of the phenomenon? Not sure such statements are relevant for quantum particles.
3. "it still requires two dots to manifest because the system needs to be filled into a low-energy (subgap) triplet state, e.g. with one electron on each dot"
For me, two dots is thus a convenient model. Two dots in series can be always regarded as a single dot with, say, two levels. My guess is that the authors require a triplet ground state of either single or double dot, rather than two dots.
Anonymous Report 1 on 2021-9-20 (Invited Report)
1- It describes a simple transport blockade mechanism that is relevant and readily detectable in double dot/superconductor junctions
2- The presentation is very to-the-point, and immediately addresses the obvious question of the difference to the better known spin-blockade mechanism
3- It references experiments demonstrating the effect
4- It contains microscopic rate-equation computations and an analysis of some of the blockade breakdown mechanisms
1- Although not in this specific form, there are prior reports of analogous mechanisms, such as that in Ref , so the novelty is not so high
2- It describes a somewhat trivial effect (few would call it "groundbreaking"), although it remains an interesting twist on the spin/charge blockade story
I found the description of the Andreev blockade mechanism very clear and instructive, especially in regards to the comparison to spin blockade. It is not particularly striking or physically revealing, but it does complement our vocabulary of transport phenomena with a new useful term. Beyond discussions of their significance, all the claims seem valid on a first read. The results might not be 100% original, since the mechanism is so obvious that anybody dealing with double dot in series with a superconductor is bound to have encountered this. The authors themselves mention Ref  which is rather close. This paper was posted in the arXiv before Ref , but the latter has already been published. Nothing to add on the subject of presentation, it is perfectly adequate and focused.
I cannot suggest any improvements to the manuscript, as formally it is complete and well crafted. The only problem is with originality and significance, which cannot be addressed by incremental improvements.