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Latest News

Quantum interference of identical photons from remote GaAs quantum dots

Recently published in Nature Nanotechnology, we demonstrate quantum interference between single photons from separate quantum dots. Such a demonstration has been attempted multiple times in the past decade and appeared challenging. The problem is the noise: the noise affects the photon creation process of different quantum dots in different ways. Thus, single photons created by separate quantum dots are sometimes distinguishable. Low-noise GaAs quantum dots are employed for our work, each operated in an independent cryostat. Single photons are created from two distant quantum dots and simultaneously sent to two inputs of a beamsplitter. Despite their (different) origins, the photons exhibit bunching in the beamsplitter output with 93% visibility: they are almost identical. Using an optical CNOT operation, we achieve high-fidelity entanglement between photons from two quantum dots. Our results establish low-noise GaAs quantum dots as interconnectable sources of identical photons.

Quantum interference of identical photons from remote GaAs quantum dots

A diamond-confined open microcavity featuring a high quality-factor and a small mode-volume

In out recent publication in Journal of Applied Physics, we report on an open microcavity containing a diamond micromembrane. Despite operation in the so-called diamond confined regime, where the electric field profile inside the cavity is maximized across the diamond-air interface, we demonstrate quality factors exceeding 120 000. We next develop a qualitative model describing the losses in our cavity and determine that the dominant source of losses to be surface waviness – surface textures with dimensions comparable to the cavity beam waist. The large quality factor combined with a small mode volume of 3.9λ03, yield a predicted Purcell factor of 170, a significant improvement over the state-of-the-art.

A diamond-confined open microcavity featuring a high quality-factor and a small mode-volume

A chiral one-dimensional atom using a quantum dot in an open microcavity

In our recent publication in npj Quantum Information we have demonstrated a chiral one-dimensional atom using a single semiconductor quantum dot in a tunable microcavity. In a chiral atom, photons propagating in one direction interact with the atom, while photons propagating in the other direction do not. Here, we achieve strong non-reciprocal absorption of single-photons, a single-photon diode. Proof that chirality arises from a single emitter is found in the nonlinear behaviour at low powers – light propagating in the backward direction of the diode is highly bunched.

A chiral one-dimensional atom using a quantum dot in an open microcavity

A hole spin qubit in a fin field-effect transistor above 4 kelvin

One of the greatest challenges in quantum computing is scalability. Classical computing overcome this problem by integrating bilions of nm-scale fin field-effect transistors (FinFETs) on a silicon chip. Here, we operate a silicon FinFET as a hole spin qubit above 4 K. At this elevated temperature cooling power increases by order of magnitudes compared to typical qubit operation temperatures, such that on-chip integration with control electronics becomes feasible. We achieve fast electrical 3-axis control with speeds up to 150 MHz, single-qubit fidelities at the fault-tolerance threshold, and a Rabi quality factor greater than 87. The devices feature both industry compatibility and quality, yet are fabricated in a flexible and agile way accelerating future development. The work was published in Nature Electronics.

A hole spin qubit in a fin field-effect transistor above 4 kelvin

Richard receives the Nevill Mott Medal and Prize from IOP!

Prof. Richard Warburton received the prestigious Nevill Mott Medal and Prize from the Institute of Physics (UK)! The prize was awarded in recognition of his outstanding research in solid-state physics and quantum optics, especially the invention and application of Coulomb blockade devices to create coherent spin-photon interfaces and quantum light sources. Congratulations!

Read more here: https://www.iop.org/about/awards/2021-nevill-mott-medal-and-prize

Richard receives the Nevill Mott Medal and Prize from IOP!

Optically driving the radiative Auger transition

Radiative Auger is a process that leads to red-shifted satellite peaks in the emission of atoms and solid-state quantum emitters. It is caused by Coulomb interactions between charged carriers. In our recent paper in Nature Communications, we show for the first time that it is possible to turn the whole process around by optical driving of the radiative Auger transition. Possible applications could be fast optical switching or THz spectroscopy.

Optically driving the radiative Auger transition

Nadine Leisgang wins the Nano Image Award 2021!

Nadine Leisgang received the Nano Image Award 2021 for the optical micrograph image of a gated van der Waals heterostructure. The device consists of two monolayers of transition metal dichalcogenides encapsulated between insulating hexagonal boron nitride flakes. Direct gold contacts allow tuning the carrier concentration in the optically active layers in the middle of the structure. Few-layer graphene sheets on the top and bottom of the stack serve as local gates to apply an electric field across the device.

This image reflects the complexity and – at the same time – the beauty of the fabrication of van der Waals heterostructures.

Nadine Leisgang wins the Nano Image Award 2021!

Laser writing of low-charge-noise nitrogen-vacancy centers in diamond

In our recent publication in ACS Photonics, we report on the pulsed-laser-induced generation of high-quality nitrogen-vacancy (NV) centers in diamond facilitated by a solid-immersion lens (SIL). The SIL enables laser writing at energies as low as 5.8 nJ per pulse and allows vacancies to be formed close to a diamond surface without inducing surface graphitization. We present samples in which NV center arrays were laser-written across the full diamond thickness, all presenting narrow optical linewidth distributions with means down to 62.1 MHz. The linewidths include the effect of long-term spectral diffusion induced by a 532 nm repump laser for charge-state stabilization, underlining the extremely low charge-noise environment of the created color centers.

Laser writing of low-charge-noise nitrogen-vacancy centers in diamond
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