Decoherence Control of Nitrogen-Vacancy Centers.

Quantum mechanical systems lose coherence through interacting with external environments-a process known as decoherence. Although decoherence is detrimental for most of the tasks in quantum information processing, a substantial degree of decoherence is crucial for boosting the efficiency of quantum processes, for example, in quantum biology and other open systems. The key to the success in simulating those open quantum systems is therefore the ability of controlling decoherence, instead of eliminating it.

Direct Measurement of Topological Numbers with Spins in Diamond.

Topological numbers can characterize the transition between different topological phases, which are not described by Landau's paradigm of symmetry breaking. Since the discovery of the quantum Hall effect, more topological phases have been theoretically predicted and experimentally verified. However, it is still an experimental challenge to directly measure the topological numbers of various predicted topological phases.

Generating giant and tunable nonlinearity in a macroscopic mechanical resonator from a single chemical bond.

Nonlinearity in macroscopic mechanical systems may lead to abundant phenomena for fundamental studies and potential applications. However, it is difficult to generate nonlinearity due to the fact that macroscopic mechanical systems follow Hooke's law and respond linearly to external force, unless strong drive is used. Here we propose and experimentally realize high cubic nonlinear response in a macroscopic mechanical system by exploring the anharmonicity in chemical bonding interactions.

Experimental Realization of High-Efficiency Counterfactual Computation.

Counterfactual computation (CFC) exemplifies the fascinating quantum process by which the result of a computation may be learned without actually running the computer. In previous experimental studies, the counterfactual efficiency is limited to below 50%. Here we report an experimental realization of the generalized CFC protocol, in which the counterfactual efficiency can break the 50% limit and even approach unity in principle.

High-resolution vector microwave magnetometry based on solid-state spins in diamond.

The measurement of the microwave field is crucial for many developments in microwave technology and related applications. However, measuring microwave fields with high sensitivity and spatial resolution under ambient conditions remains elusive. In this work, we propose and experimentally demonstrate a scheme to measure both the strength and orientation of the microwave magnetic field by utilizing the quantum coherent dynamics of nitrogen vacancy centres in diamond.

Protein imaging. Single-protein spin resonance spectroscopy under ambient conditions.

Magnetic resonance is essential in revealing the structure and dynamics of biomolecules. However, measuring the magnetic resonance spectrum of single biomolecules has remained an elusive goal. We demonstrate the detection of the electron spin resonance signal from a single spin-labeled protein under ambient conditions.

Experimental realization of a compressed quantum simulation of a 32-spin Ising chain.

Certain n-qubit quantum systems can be faithfully simulated by quantum circuits with only O(log(n)) qubits [B. Kraus, Phys. Rev.

Implementation of dynamically corrected gates on a single electron spin in diamond.

Precise control of an open quantum system is critical to quantum information processing but is challenging due to inevitable interactions between the quantum system and the environment. We demonstrated experimentally a type of dynamically corrected gates using only bounded-strength pulses on the nitrogen-vacancy centers in diamond. The infidelity of quantum gates caused by a nuclear-spin bath is reduced from being the second order to the sixth order of the noise-to-control-field ratio, which offers greater efficiency in reducing infidelity.

Demonstration of motion transduction based on parametrically coupled mechanical resonators.

Universal sensing of the motion of mechanical resonators with high precision and low backaction is of paramount importance in ultraweak signal detection, which plays a fundamental role in modern physics. Here we present a universal scheme that mechanically transfers the motion of the resonator not directly measurable to the one that can be precisely measured using mechanical frequency conversion. Demonstration of the scheme at room temperature shows that both the motion imprecision and the backaction force are below the intrinsic level of the objective resonator, which agrees well with our theoretical prediction.

Quantum games of asymmetric information.

We investigate quantum games in which the information is asymmetrically distributed among the players and find that the possibility of the quantum game outperforming its classical counterpart depends strongly on not only the entanglement but also the informational asymmetry. What is more interesting, when the information distribution is asymmetric, is that the contradictive impact of the quantum entanglement on the profits is observed, which is not reported in quantum games of symmetric information.