Jing Yan Haw

Replicating the benefits of Deutschian closed timelike curves without breaking causality

Sending messages back in time can be remarkably powerful, even if no one ever reads them, says an international research team. Peculiarities of general relativity called ‘closed timelike curves’ (CTCs) effectively allow particles to travel backwards in time, and are consistent with current quantum theory. However, CTCs break causality, the fundamental notion that cause must precede effect, and thus their existence remains highly controversial. Mile Gu at Tsinghua University in China and colleagues in Australia, Singapore, the UK and Canada investigated ‘open timelike curves’ (OTCs), which keep all time-travelling particles isolated from the past and thus respect causality. The researchers showed that despite such restrictions, OTCs allow quantum computers to clone quantum states, defy Heisenberg’s uncertainty principle, and efficiently solve previously intractable mathematical problems. This greatly improves prospects for relativistically enhanced quantum computation.

Surpassing the no-cloning limit with a heralded hybrid linear amplifier for coherent states

The no-cloning theorem states that an unknown quantum state cannot be cloned exactly and deterministically. However, this limit can be circumvented by abandoning determinism and using probabilistic methods. Here, we report an experimental demonstration of probabilistic cloning of arbitrary coherent states that clearly surpasses the no-cloning limit. Our scheme is based on a hybrid linear amplifier that combines an ideal deterministic linear amplifier with a heralded measurement-based noiseless amplifier. We demonstrate the production of up to five clones with the fidelity of each clone clearly exceeding the corresponding no-cloning limit. Moreover, since successful cloning events are heralded, our scheme has the potential to be adopted in quantum repeater, teleportation and computing applications.

Overarching framework between Gaussian quantum discord and Gaussian quantum illumination

We are grateful for funding from the National Research Foundation of Singapore (NRF Award No. NRF-NRFF2016- 02), the John Templeton Foundation Grant No. 53914 “Occam’s Quantum Mechanical Razor: Can Quantum theory admit the Simplest Understanding of Reality?”, the Foundational Questions Institute, and the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (Project No. CE110001027). This material is based on research supported in part by the National Research Foundation of Singapore under NRFAward No. NRF-NRFF2013-01. S.T. acknowledges support from the AFOSR under Grant No. FA2386-15-1-4082.

Surpassing the no-cloning limit with a heralded hybrid linear amplifier

The no-cloning theorem states that an unknown quantum state cannot be cloned exactly and deterministically. However, this limit can be circumvented by abandoning determinism and using probabilistic methods. Here, we report an experimental demonstration of probabilistic cloning of arbitrary coherent states that clearly surpasses the no-cloning limit. Our scheme is based on a hybrid linear amplifier that combines an ideal deterministic linear amplifier with a heralded measurement-based noiseless amplifier. We demonstrate the production of up to five clones with the fidelity of each clone clearly exceeding the corresponding no-cloning limit. Moreover, since successful cloning events are heralded, our scheme has the potential to be adopted in quantum repeater, teleportation and computing applications.

Quantum enhancement of signal-to-noise ratio with a heralded linear amplifier

Due to the pervasive nature of decoherence, protection of quantum information during transmission is of critical importance for any quantum network. A linear amplifier that can enhance quantum signals stronger than their associated noise while preserving quantum coherence is therefore of great use. This seemingly unphysical amplifier property is achievable for a class of probabilistic amplifiers that does not work deterministically. Here we present a linear amplification scheme that realises this property for coherent states by combining a heralded measurement-based noiseless linear amplifier and a deterministic linear amplifier. The concatenation of two amplifiers introduces the flexibility that allows one to tune between the regimes of high-gain or high noise-reduction, and control the trade-off of these performances against a finite heralding probability. We demonstrate an amplification signal transfer coefficient of

Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution

\mathcal{T}_s > 1

Experimental verification of quantum discord in continuous-variable states and operational significance of discord consumption

with no statistical distortion of the output state. By partially relaxing the demand of output Gaussianity, we can obtain further improvement to achieve a

Machine Learning Cryptanalysis of a Quantum Random Number Generator

\mathcal{T}_s = 2.55 \pm 0.08

Integrated Chip for Continuous-variable Quantum Key Distribution using Silicon Photonic Fabrication

. Our amplification scheme only relies on linear optics and post-selection algorithm. We discuss the potential of using this amplifier as a building block in extending the distance of quantum communication.