IONQUANSENSE · Quantum information and sensing schemes for trapped ions

Quantum information and sensing schemes for trapped ions

We have studied the foundations of future quantum technologies. In particular, we studied and proposed theoretical methods to probe, extend and control coherence. Exploiting coherence, we investigated its prospects for technological use, mainly for quantum simulations, precise measurements and polarization. Our work included theoretical proposals for the implementation of quantum technologies via various platforms, concentrating on NV centers in diamond and trapped ions. We extensively collaborated with experimental groups from various fields on the realization of quantum technology goals. The IonQuanSense deals with the realisation of robust quantum operations by dynamical decoupling and error correction and applying these for quantum simulations and quantum sensing. Construction of a protected qubit — In this project we presented a new general scheme for the construction of a protected qubit subspace. The scheme, which is suitable for levels with either half-integer or integer angular momentum states, utilizes a multi-state structure, on which continuous dynamical decoupling fields are applied. The scheme can be realized with state-of-the-art experimental setups, and should be able to push the coherence time to the lifetime limit. Moreover, it is suitable for a wide range of solid-state and atomic systems, and it is applicable to a variety of tasks in the field of quantum information such as quantum sensing, quantum magnetometery, and quantum memories. We analyzed the performance of the scheme for the case composed of trapped ions, and showed how single qubit gates and an ensemble coupling to a cavity mode can be implemented efficiently. Moreover, we have developed a scheme in which this structure could be used in a reversed situation in which this protection could decouple the electron spin from the nucleus and thus extend the coherence time of the nucleus. Quantum Simulations— In this project we proposed how to realize a quantum simulation of the Haldane phase in trapped ions. More specifically, we developed a protocol to simulate the Haldane phase which exists in the Heisenberg region of the spin-one XXZ antiferromagnetic chain, where the spin is modeled via the three-level hyperfine structure in the microwave regime, and the interaction is achieved by the use of large magnetic field gradients that compensate the presence of a very small Lamb-Dicke parameter when using microwave sources. By reverse engineering we show how to generate all the terms in the simulated Hamiltonian using five microwave driving fields. We explained how to reach the Haldane phase adiabatically, starting from the large D phase where the ground states are robust to magnetic and Rabi frequency fluctuations, namely, they belong to the decoherence-free subspace. The verification of the Haldane phase can be achieved by measuring its characteristics: an excitation gap and exponentially decaying correlations, a nonvanishing nonlocal string order and a double-degenerated entanglement spectrum. In higher dimensions this platform gives rise to new research exploring quantum spin liquid phases that exhibit long-range entanglement patterns and hidden global topological orders. Their highly nonlocal ground states would be robust to local noise sources, giving rise to the realization of topologically protected quantum computation. Quantum sensing — The goal of this project is to develop an optimal method for measuring the distance between a NV centre in diamond and an external nuclear spin. To determine this distance, a continuous microwave driving field or a set of microwave pulses are applied which make the NV spin sense the nuclear spin due to the dipole dipole interaction between them. We have developed an optimal method which will determine the distance between the NV center and target nuclear spin to the best accuracy and with minimal experimental resources.

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