Controlling the interaction of a single quantum system with its environment is a fundamental challenge in quantum science and technology. We strongly suppressed the coupling of a single spin in diamond with the surrounding spin bath by using double-axis dynamical decoupling. The coherence was preserved for arbitrary quantum states, as verified by quantum process tomography. The resulting coherence time enhancement followed a general scaling with the number of decoupling pulses. No limit was observed for the decoupling action up to 136 pulses, for which the coherence time was enhanced more than 25 times compared to that obtained with spin echo. These results uncover a new regime for experimental quantum science and allow us to overcome a major hurdle for implementing quantum information protocols.

rates. Here we present the integration of dynamical decoupling into quantum gates for a paradigmatic hybrid system, the electron-nuclear spin register. Our design harnesses the internal resonance in the coupled-spin system to resolve the conflict between gate operation and decoupling. We experimentally demonstrate these gates on a two-qubit register in diamond operating at room temperature. Quantum tomography reveals that the qubits involved in the gate operation are protected as accurately as idle qubits. We further illustrate the power of our design by executing .Decoherence is a major hurdle towards realizing scalable quantum technologies in the solid state. The inter-qubit dynamics that implement the quantum logic are unavoidably affected by uncontrolled couplings to the solid-state environment, preventing high-fidelity gate performance (Fig 1a). Dynamical decoupling 4 , a technique that employs fast qubit flips to average out the interactions with the environment, is a powerful and practical tool for mitigating decoherence [5][6][7][8][9][10][11][12]24,25 . This approach is particularly promising for the emerging class of hybrid quantum architectures [13][14][15][16][17][18][19][20][21][22][23] in which different types of qubits, such as electron and nuclear spins, superconducting resonators, and nanomechanical oscillators, perform different functions. Dynamical 2 decoupling allows for each qubit type to be decoupled at its own appropriate rate, ensuring uniform coherence protection.However, combining dynamical decoupling with quantum gate operations is generally problematic, since decoupling does not distinguish the desired inter-qubit interaction from the coupling to the decohering environment, and in general cancels both (Fig. 1b). For hybrid systems, where large difference in coherence and control timescales among the different qubit types make the encoding-based schemes 11 or synchronized application of decoupling pulses 4,12 fail, a solution has thus far remained elusive.Here we present a design that enables the integration of decoupling into gate operation for hybrid quantum architectures. We demonstrate such decoherence-protected gates on a prototype hybrid quantum system: a two-qubit register consisting of an electron and a nuclear spin (Fig. 1c). The key idea is to precisely adapt the time intervals between the electron decoupling pulses to the nuclear spin dynamics. When combined with continuous nuclear spin driving, this synchronization yields selective rotations of the nuclear spin while the electron spin is dynamically protected, as explained below. This design preserves all of the advantages of dynamical decoupling without requiring additional qubits or controllable inter-qubit couplings. It can be readily implemented to yield decoherence-protected quantum gates in a range of hybrid systems, such as various electron-nucleus spin registers [13][14][15][16][17]20 , and interface gates between the qubits and a spinchain quantum databus 22,23 .We experimentally demonstrate the scheme on ...