Session P29: Semiconducting QC Architectures and Quantum Photonics

Full 300mm fin based QD device characterization

Intel’s efforts towards the fabrication of spin qubit devices have required a comprehensive device characterization, from transistors and quantum dots, to qubits, which have been co-fabricated in the same die/wafer. In this talk, we will present an in-depth device characterization, and the results from quantum dot devices manufactured in a full 300mm line. We will give details of the fin based process flow which yields high charging energy devices. The extraction of QD related figures of merit from room and low temperature testing (1.6K) are part of the method to rapidly screen 300mm wafers with thousands of devices which are used to determine the spin qubit devices that will be taken to the milli-kelvin measurements; keeping up with the pace of the 300mm fab output.   

Simulating Nagaoka Ferromagnetism in a 2×2 Quantum Dot Array

The Fermi-Hubbard model provides a description of interacting electrons in a lattice. The interaction between electrons in arrays of electrostatically defined quantum dots is naturally described by a Fermi-Hubbard Hamiltonian; moreover, the high-degree of tunability in these systems make them a perfect platform to explore different regimes of the Hubbard model through analogue quantum simulations¹.

Last year we established a 2x2 gate-defined quantum dot array as a promising solid-state analogue quantum simulator². Here we present results on simulation of Nagaoka Ferromagnetism in this system. We experimentally observe a ferromagnetic ground state in an almost-half-filled lattice, as predicted³. We use the high-levels of control in our system to manipulate the Hamiltonian parameters and perform measurements that test the validity of our observations. For example, breaking the periodic boundary condition gets rid of the ferromagnetic ground state altogether. To our knowledge, this is the first experimental verification of Nagaoka’s prediction as well as the first simulation of magnetism using quantum dot arrays.

[1] T. Hensgens, et. al., Nature 548, 70 (2017)
[2] U. Mukhopadhyay, et. al., Appl. Phys. Lett. 112, 183505 (2018)
[3] Y. Nagaoka, Phys. Rev. 147, 392-405 (1966)   

Coherent control of individual electron spins in a two-dimensional array of tunnel coupled quantum dots

Controlling nanocircuits at the single electron spin level in quantum dot arrays is at the heart of any scalable spin-based quantum information platform. The cumulated efforts to finely control individual electron spins in linear arrays of tunnel coupled quantum dots have permitted the recent coherent control of multi-electron spins and the realization of quantum simulators. However, the two-dimensional scaling of such control is a crucial requirement for simulating complex quantum matter and for efficient quantum information processing, and remains up to now a challenge.
Here we demonstrate such two-dimensional coherent control using individual electron spins in arrays up to 9 tunnel-coupled lateral quantum dots. Two-electron spin initialization, spin readout and spin transfer enable exploration of the spin dynamics in the QDs array. We demonstrate a procedure that permits local enhancement of the tunnel coupling between two dots of the array up to a range where coherent exchange oscillations, the basis of the two-qubit gates for electron spin qubits, are observed. Taking advantage of the tunability of the structure, we finally realize complex and multi-directional displacements of one and two electrons through quantum dot arrays. This work demonstrates key quantum functionalities, crucial for using two-dimensional quantum dot arrays for quantum simulation and computation.

[1] H. Flentje, P.-A. Mortemousque, R. Thalineau, A. Ludwig, A. D. Wieck, C. Bäuerle, T.
Meunier, Coherent long-distance displacement of individual electron spins, Nat. Comm.
8, 501 (2017).
[2] P.-A. Mortemousque, H. Flentje, E. Chanrion, A. Ludwig, A. D. Wieck, M. Urdampilleta,
C. Bäuerle, T. Meunier, Coherent control of individual electron spins in a
two-dimensional array of quantum dots, Arxiv : 1809.04584   

A large-scale single-photon source and spin qubit arrays in a photonic integrated chip

Single-photon sources are essential components in a variety of optical quantum technologies. We demonstrate a large array of single-photon sources and spin qubits on a single photonic chip. Our single-photon source array is composed of color centers in a monolithic diamond nanophotonic structure that is efficiently coupled to a photonic integrated circuit. Additionally, the long-lived spin states of color centers in diamond may serve as quantum memories in a repeater network.   

On-chip Integrable Spectrally Uniform Ordered Quantum Dot Single Photon Source Array with High Emission Purity (>98.99%) for Scalable Quantum Optical Networks

Towards the goal of building scalable on-chip optical networks we have proposed a new paradigm that integrates an array of mesa top single quantum dot (MTSQD) single photon sources (SPSs) with dielectric light manipulating units (LMUs) [1]. We demonstrated InGaAs/GaAs MTSQDs in 5x8 array [1] showing remarkably improved spectral uniformity than the typically studied self-assembled island QDs but, more importantly, several pairs of MTSQDs exhibit emission wavelengths within 300μeV, the instrument resolution [2]. The measured single photon emission purity was thus limited to 90% at 9K. In this talk we report studies with improved high resolution of ~10μeV demonstrating single photon emission purity > 98.99% (g⁽²⁾(0)<0.02) in these MTSQDs at 9.4K. The MTSQD neutral exciton’s intrinsic linewidth and fine structure splitting are found to be ~10µeV and <10µeV, respectively. The results highlight the potential of the spatially-ordered MTSQDs-LMU integrated system for realizing quantum optical circuits[3]. Work on examining photon indistinguishability and coherence is underway.
[1] Jiefei Zhang et.al, J. Appl. Phys. 120, 243103 (2016)
[2] Jiefei Zhang et.al, APS March (2017)
[3] S. Chattaraj, arXiv:1712.09700v2(2018)
  

Tuning Photonic Crystal Cavity Resonances with Phase Change Material GeTe

Photonic crystal slabs are a promising architecture for a variety of computational and sensor architectures including quantum computers and neuromorphic networks. Such devices consist of a 2-D membrane of cavities and waveguides with embedded quantum dots (QDs). While many advances such as demonstrations of indistinguishable single photon sources and quantum entanglement have been shown, such devices are still difficult to scale as a network. The primary limitations are from natural variations during material growth and device fabrication, which cause resonances of the QDs and cavities to span energies much larger than their linewidths. One solution is to use capping layers which can tune the underlying device, changing properties such as strain and effective index of refraction, and whose structural phase can be locally altered using laser annealing, potentially allowing for local tuning of QDs or cavities. We show results of using thin films of such a phase change material, GeTe, to tune cavity resonances independent of local QDs in such devices. This tuning is dependent on the original resonance energy of the cavity and the amount of material deposited.   

Integrated Quantum Networks of Mie-resonance based All-Dielectric Optical Circuits with Single Photon Sources for Quantum Entanglement

Recently we introduced [1] a new approach to on-chip optical circuits based on subwavelength scale dielectric building blocks (DBBs) metastructures integrated with single photon sources (SPSs) such as the mesa-top single quantum dot (MTSQD) ordered array [1] in which a single collective Mie resonance of the DBB metastructure provides all needed five light manipulating functions [2]: (1) SPS emission rate enhancement, (2) emission directionality, (3) wave-guiding (4) beam-splitting and (4) beam-combining. The simulations reported were for spherical DBBs as it enables analytical calculations [1]. The lithographic fabrication of such structures will have rectangular DBBs and thus in this talk we present the design and simulation of networks of rectangular DBBs, co-designed for monolithic integration with GaAs/InGaAs MTSQD SPS arrays such that every MTSQD is coupled to the same single collective mode of the network. Finite element based simulation results for such networks with coupled SPSs will be presented that suggest quantum effects such as path-entanglement and super-radiance– constituting a step towards quantum information processing.
[1] J. Zhang et.al, J. Appl. Phys. 120, 243103(2016)
[2] S. Chattaraj, arXiv:1712.09700v2(2018)   

Optical locking of a quantum dot electron spin qubit

InGaAs quantum dots (QDs) can function as solid state quantum network nodes, offering a field-leading interface between a single spin and an optical mode [1]. Exploiting this interface requires complete control of a QD spin, to tailor spin-photon entanglement in such a network. Whilst the rotations offered by the current state of the art are highly coherent [2], full SU(2) control relies on varying delays between sequential pulses, limiting the scheme to simple few-gate sequences.
Spectral splitting of a laser into two sidebands through modulation allows us to resonantly address a Raman transition between the two ground states of a spin in our QD. This all-optical scheme gives direct access to the phase and frequency of the field linking our states, releasing us from the need for well-defined sequence delays. We use Rabi oscillations and Ramsey interferometry to demonstrate complete control of our Rabi vector.
This enables us to perform spin-locking, protecting our qubit state for longer than the homogeneous dephasing time and allowing high-fidelity gates on this timescale. Our work represents versatile spin control and provides a way towards on-chip all-optical spin manipulation.
[1] Somaschi, N. et al, Nat. Photonics 10 340-345 (2016)
[2] Press, D. et al, Nature 456 218-221 (2008)
  

4H-SiC-on-Insulator Platform for Quantum Photonics with Color Centers

Defects in Silicon Carbide (SiC) are considered for quantum photonics applications because of their favorable spin coherence properties and optical emission wavelengths. To aid integration of these defects into nanophotonic structures, we develop a 4H-SiC-on-insulator platform based on bonding and thinning techniques. The process results in 4H-SiC films of pristine crystal quality with no radiative defects in the 800 - 1000 nm wavelength range. Color centers are readily introduced via irradiation. We demonstrate 4H-SiC ring resonators and photonic crystal cavities with Q ~ 10⁴   

Scalable frequency locking of single photon sources for quantum photonic technologies

Large-scale quantum technologies require exquisite control over many individual quantum systems. Typically, such systems are very sensitive to environmental fluctuations, and diagnosing errors via measurements causes unavoidable perturbations. Here we present an in situ frequency locking technique that monitors and corrects frequency variations in single photon sources based on microring resonators. By using the same classical laser fields required for photon generation as a probe to diagnose variations in the resonator frequency, our protocol applies feedback control to correct photon frequency errors in parallel to the optical quantum computation without disturbing the physical qubit. We implement our technique on a silicon photonic device and demonstrate feedback controlled quantum state engineering. Our approach enables frequency locking of many single photon sources for large-scale photonic quantum technologies.   

Event-ready entangled photons from a solid-state single-photon source.

Solid-state emitters, such as semiconductor quantum dots, are a promising platform to develop single-photon sources. Recent breakthroughs in material syntheses and fabrication processes led to a new generation of devices, combining high emission brightness with near unity indistinguishable pure single-photon output [1]. These new generation single-photos sources are staring to enable experiments with multiple indistinguishable photons [2], a key step towards large-scale optical quantum technologies.

Here we employ a quantum dot source to demonstrate a 4-qubit Type-II Fusion Entangling Gate [4]. The Type-II Fusion Gate relies on the conditional detection of two ancillary qubits to generate entanglement between the two remaining qubits. We study the performance of this entangling gate as a function of the single-photon indistinguishability. We also discuss potential applications tor the Type-II fusion gate as an event-ready souce entangled photons.


[1] N. Somaschi, et al, “Near-optimal single-photon sources in the solid state” Nat. Phot. 10, 340 (2016)
[2] J. Loredo, J., et al, “Scalable performance in solid-state single photon sources”, Optica, 3, (2016).
[3] D. E. Browne, and T. Rudolph, “Resource-efficient linear optical quantum computation”, Phys. Rev. Lett. 95, 010501 (2005).   

Optimized Quantum Photonics in Diamond

Diamond hosts a variety of quantum emitters and is thus a promising material platform for applications in quantum information processing and quantum sensing. Such quantum technologies will likely operate at the level of single or few photons. Therefore, they require highly efficient integrated photonic circuits to harness the full potential of the excellent optical properties of color centers in diamond. However, state-of-the-art design and fabrication techniques for diamond devices in quantum optics strongly limit the geometry and variety of the device components. We utilize inverse design optimization and fabrication methods based on quasi-isotropic etching to significantly improve on efficiency, scalability, and functionality of diamond photonics. To showcase the significance of these advances, we solve outstanding design challenges, such as optical free space interfaces and improve on efficiency and scalability of diamond photonics.