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Continuous-variable (CV) bosonic quantum systems are extremely appealing for encoding quantum information as they not only offer an infinite Hilbert space for establishing error-resilient codespaces, but their flexible implementation over a variety of degrees of freedom also permits their wide application range in quantum information and computation tasks. Quantum error mitigation and suppression are important resource-efficient techniques to reduce errors due to noise that could corrupt these quantum systems. 

In this talk, I will introduce feasible linear-optical methods to mitigate thermal and random-displacement noise. Using photon-subtraction gadgets with linear attenuation/amplification capabilities, we proved that probabilistic error cancellation can be used to reinforce interference features of a CV quantum state in order to protect it against these noise channels. Next, I shall also propose a linear-optical suppression procedure (multimode beam splitter and vacuum measurements) to coherently and significantly suppress dephasing noise, a crucial problem in quantum information/computation tasks. No high-order nonlinearities, like the Kerr effect, are required and numerical results show that the two-mode beamsplitter scheme is already sufficient for demonstrating significant dephasing suppression for all tested bosonic quantum codes. Furthermore, we successfully proved that dephasing noise can be *completely* nullified with easy-to-realize asymptotically-large interferometers (implementable via beam splitters and phase shifters), vacuum measurements and linear amplification at nonvanishing success rates. After introducing these linear-optical procedures, we showed that arbitrary noise compositions can also be mitigated by combining the procedures through leveraging their compatibility (commutativity). All success probabilities for mitigating and suppressing both idling and universal-gate noise are high for quantum bosonic codes that are commonly considered, rendering them realistically implementable. Last but not the least, we numerically show that for reasonable noise strengths, error mitigation and suppression are also possible when universal-gate operations are performed within the mitigation/suppression passage. This further showcases the universality of this work.