Brotons-Gisbert Mauro, Branny Artur, Kumar Santosh, Picard Raphaël, Proux Raphaël, Gray Mason, Burch Kenneth S, Watanabe Kenji, Taniguchi Takashi, Gerardot Brian D
Institute of Photonics and Quantum Sciences, SUPA, Heriot-Watt University, Edinburgh, UK.
Department of Applied Physics, Royal Institute of Technology, Stockholm, Sweden.
Nat Nanotechnol. 2019 May;14(5):442-446. doi: 10.1038/s41565-019-0402-5. Epub 2019 Mar 11.
Gate-tunable quantum-mechanical tunnelling of particles between a quantum confined state and a nearby Fermi reservoir of delocalized states has underpinned many advances in spintronics and solid-state quantum optics. The prototypical example is a semiconductor quantum dot separated from a gated contact by a tunnel barrier. This enables Coulomb blockade, the phenomenon whereby electrons or holes can be loaded one-by-one into a quantum dot. Depending on the tunnel-coupling strength, this capability facilitates single spin quantum bits or coherent many-body interactions between the confined spin and the Fermi reservoir. Van der Waals (vdW) heterostructures, in which a wide range of unique atomic layers can easily be combined, offer novel prospects to engineer coherent quantum confined spins, tunnel barriers down to the atomic limit or a Fermi reservoir beyond the conventional flat density of states. However, gate-control of vdW nanostructures at the single particle level is needed to unlock their potential. Here we report Coulomb blockade in a vdW heterostructure consisting of a transition metal dichalcogenide quantum dot coupled to a graphene contact through an atomically thin hexagonal boron nitride (hBN) tunnel barrier. Thanks to a tunable Fermi reservoir, we can deterministically load either a single electron or a single hole into the quantum dot. We observe hybrid excitons, composed of localized quantum dot states and delocalized continuum states, arising from ultra-strong spin-conserving tunnel coupling through the atomically thin tunnel barrier. Probing the charged excitons in applied magnetic fields, we observe large gyromagnetic ratios (∼8). Our results establish a foundation for engineering next-generation devices to investigate either novel regimes of Kondo physics or isolated quantum bits in a vdW heterostructure platform.
粒子在量子受限态与附近离域态费米库之间的门控可调谐量子力学隧穿，为自旋电子学和固态量子光学的许多进展奠定了基础。典型的例子是一个半导体量子点，它通过一个隧道势垒与一个门控接触电极隔开。这使得库仑阻塞得以实现，即电子或空穴可以逐个加载到量子点中的现象。根据隧道耦合强度，这种能力有助于实现单自旋量子比特或受限自旋与费米库之间的相干多体相互作用。范德华（vdW）异质结构可以轻松组合各种独特的原子层，为设计相干量子受限自旋、降至原子极限的隧道势垒或超越传统平坦态密度的费米库提供了新的前景。然而，要释放vdW纳米结构的潜力，需要在单粒子水平上对其进行门控。在此，我们报道了一种vdW异质结构中的库仑阻塞现象，该异质结构由一个过渡金属二卤化物量子点通过原子级薄的六方氮化硼（hBN）隧道势垒与石墨烯接触电极耦合而成。得益于可调谐的费米库，我们可以确定性地将单个电子或单个空穴加载到量子点中。我们观察到由局域量子点态和离域连续态组成的混合激子，这是通过原子级薄的隧道势垒产生的超强自旋守恒隧道耦合导致的。在施加磁场中探测带电激子，我们观察到了较大的旋磁比（约为8）。我们的结果为设计下一代器件奠定了基础，以便在vdW异质结构平台上研究近藤物理的新机制或孤立量子比特。
