Quantum computation provides great speedup over its classical counterpart for certain problems. One of the key challenges for quantum computation is to realize precise control of the quantum system in the presence of noise. Control of the spin-qubits in solids with the accuracy required by fault-tolerant quantum computation under ambient conditions remains elusive. Here, we quantitatively characterize the source of noise during quantum gate operation and demonstrate strategies to suppress the effect of these. A universal set of logic gates in a nitrogen-vacancy centre in diamond are reported with an average single-qubit gate fidelity of 0.999952 and two-qubit gate fidelity of 0.992. These high control fidelities have been achieved at room temperature in naturally abundant 13C diamond via composite pulses and an optimized control method.

Control of molecular spins and their readout with a solid-state qubit are described as a unit cell in a quantum spin network.

Quantum control of systems plays an important role in modern science and technology. The ultimate goal of quantum control is to achieve high-fidelity universal control in a time-optimal way. Although high-fidelity universal control has been reported in various quantum systems, experimental implementation of time-optimal universal control remains elusive. Here, we report the experimental realization of time-optimal universal control of spin qubits in diamond. By generalizing a recent method for solving quantum brachistochrone equations [X. Wang et al., Phys. Rev. Lett. 114, 170501 (2015)], we obtained accurate minimum-time protocols for multiple qubits with fixed qubit interactions and a constrained control field. Single- and two-qubit time-optimal gates are experimentally implemented with fidelities of 99% obtained via quantum process tomography. Our work provides a time-optimal route to achieve accurate quantum control and unlocks new capabilities for the emerging field of time-optimal control in general quantum systems.

The adiabatic quantum computation is a universal and robust method of quantum computing. In this architecture, the problem can be solved by adiabatically evolving the quantum processor from the ground state of a simple initial Hamiltonian to that of a final one, which encodes the solution of the problem. By far, there is no experimental realization of adiabatic quantum computation on a single solid spin system under ambient conditions, which has been proved to be a compatible candidate for scalable quantum computation. In this letter, we report on the first experimental realization of an adiabatic quantum algorithm on a single solid spin system under ambient conditions. All elements of adiabatic quantum computation, including initial state preparation, adiabatic evolution, and final state readout, are realized experimentally. As an example, we factored 35 into its prime factors 5 and 7 on our adiabatic quantum processor.The nitrogen-vacancy (NV) center in diamond is an excellent quantum processor and quantum sensor at room temperature [1].The spin qubits of NV center are promising for quantum information processing due to fast resonant spin manipulation [2], long coherence time [3,4], easy initialization and read-out by laser illumination [5]. Many quantum gates [6-9], quantum algorithms [10], quantum error corrections [11,12] and quantum simulations [13,14] have been demonstrated on it. However, so far no adiabatic quantum algorithm has been realized on this system. In circuit-model quantum computation, the computational process is implemented by a sequence of quantum gates. In 2000, Farhi et al.[15] developed another architecture of quantum computation, i.e., the adiabatic quantum computing (AQC), in which the computational process can be realized through the adiabatic evolution of a system's Hamiltonian, and it is proved to be equivalent to circuit model quantum computing [16].In contrast to multiplying of large prime numbers, up to now, no efficient classical algorithm for the factorization of large number is known [17]. Previously, many experimental work on large number factorization have been done based on Shor's algorithm [18][19][20][21][22][23][24]. To demonstrate the AQC on the room temperature single spin system, we take 35 as an example and factored it on the adiabatic quantum processor. The core idea used here is to transform a factorization problem to an optimization problem and solve it under the AQC framework [25,26].Generally, to solve a problem under the AQC framework, first we need to find a problem Hamiltonian H p , and the solution of the problem is encoded in the ground state of H p . We start from the ground state of H 0 and the Hamiltonian of the evolution progress is H(t) =(1 − s(t))H 0 + s(t)H p , s(0) = 0, s(T ) = 1.(1)Where T is the total evolution time, and the whole system is governed by the Schrödinger equation

The non-Markovia dynamics of quantum evolution plays an important role in open quantum sytem. However, how to quantify non-Markovian behavior and what can be obtained from non-Markovianity are still open questions, especially in complex solid systems. Here we address the problem of quantifying non-Markovianity with entanglement in a genuine noisy solid state system at room temperature. We observed the non-Markovianity of quantum evolution with entanglement. By prolonging entanglement with dynamical decoupling, we can reveal the non-Markovianity usually concealed in the environment and obtain detailed environment information. This method is expected to be useful in quantum metrology and quantum information science.

Quantum adiabatic evolutions find a broad range of applications in quantum physics and quantum technologies. The traditional form of the quantum adiabatic theorem limits the speed of adiabatic evolution by the minimum energy gaps of the system Hamiltonian. Here, we experimentally show using a nitrogen-vacancy center in diamond that, even in the presence of vanishing energy gaps, quantum adiabatic evolution is possible. This verifies a recently derived necessary and sufficient quantum adiabatic theorem and offers paths to overcome the conventionally assumed constraints on adiabatic methods. By fast modulation of dynamic phases, we demonstrate near–unit-fidelity quantum adiabatic processes in finite times. These results challenge traditional views and provide deeper understanding on quantum adiabatic processes, as well as promising strategies for the control of quantum systems.

We experimentally resolve several weakly coupled nuclear spins in diamond using a series of novelly designed dynamical decoupling controls. Some nuclear spin signals, hidden by decoherence under ordinary dynamical decoupling controls, are shifted forward in time domain to the coherence time range and thus rescued from the fate of being submerged by the noisy spin bath. In this way, more and remoter single nuclear spins are resolved. Additionally, the field of detection can be continuously tuned on sub-nanoscale. This method extends the capacity of nanoscale magnetometry and may be applicable in other systems for high-resolution noise spectroscopy.

No abstract