Collaborative Research: Toward universal quantum computing with heterogeneously integrated quantum optical frequency combs

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Quantum computing is a disruptive technology capable of solving classically intractable problems, such as factoring integers and breaking encryption codes, and performing quantum simulations of major societal impact such as nitrogen fixation for fertilizer production, carbon dioxide fixation for carbon sequestration, and unlocking room-temperature superconductivity. The route toward full scale quantum computing faces daunting challenges. One approach away from the dominant quantum gate approach is measurement-based quantum computing, and, in particular, one-way quantum computing using cluster states. This approach circumvents the requirement of low decoherence and memories for scalability. Our approach is purely based on using photons, operates at room-temperature, and uses a wavelength compatible to present optical communication networks. Large two-dimensional cluster states will be produced using quantum optical frequency combs. These cluster states are deterministically and unconditionally generated and scale exponentially. The cluster states are based on continuous-variable quantum optical systems and are encoded over quantum fields. The key objective of this proposal is to demonstrate the generation of continuous variable cluster states on chip and to demonstrate the preparation of resource states called Gottesman-Kitaev-Preskill (GKP) grid states, which are key to error correction and to universal quantum computing. To realize the chip-scale quantum state generator, hetero-integration of different platform technology on a silicon board will be used. In particular, a high quality factor (Q) nanocavity using gratings will be realized on the SiN/SiO2 platform and will produce an optical frequency comb. A narrow linewidth semiconductor laser based on a III-V gain chip coupled to a high Q cavity will be mounted on the Si platform. Finally, a thin-film LiNbO3 modulator for high speed modulation will be heterogeneously integrated on the Si platform. A broad impact plan will be set-up to educate high school students in quantum physics, train under-represented groups in quantum engineering, and educate graduate students for success in engineering research.A realistic path to quantum computation requires the implementation of standalone chipscale systems to create and manipulate quantum states of light. These systems should ideally operate at room temperature and at wavelengths compatible with those of classical optical communication systems. In this project, a novel integrated platform to realize some basic quantum protocols with high efficiency and fidelity will be demonstrated. The proposal aims at the first realization of cluster states, cat states, and Gottesman-Kitaev-Preskill (GKP) states on a photonic chip, with the overarching goal of realizing all the required building blocks for a fault-tolerant photonic quantum computer. Measurement based quantum computation primitives, namely, feedforward on cluster states informed by field-homodyne and photon-number-resolving (PNR) detection will be realized. The experimental platform is based on one optical parametric oscillator and one electro-optic phase modulator integrated on Si. The core of the envisioned quantum system is an integrated millimeter-size grating Fabry-Perot resonator, featuring a free-spectral range of a few tens of GHz and a Q-factor better than a million at 1550 nm. The Si3N4 microresonator is pumped by a co-integrated narrow-linewidth single mode laser, and owing to the built-in Kerr nonlinearity of the medium, outputs quantum-correlated photons distributed in the spectral modes of an optical frequency comb. High-efficiency optical coupling from chip to optical fibers will be used to interface with photodetection. The first experimental objective is to demonstrate large-scale cluster state generation on chip. The second experimental objective is to demonstrate non-Gaussian (e.g. cat and GKP) state generation on chip, using PNR detection measurements. The full spectrum of possibilities of this quantum photonic chip will also be studied in microresonator optical parametric oscillators operated above threshold.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.