Demonstration of Quantum Gate Operations and Quantum Sensing on a Scalable System Based on Neutral Atoms

Neutral atoms in registers of optical tweezers have established themselves as a versatile platform for timely investigations in quantum physics. This applies in particular to the access to new orders of magnitude in metrology and the development of quantum computers. The research into quantum physics, which has been ongoing for less than a hundred years, shows potential for numerous further discoveries. This work demonstrates the application of neutral atoms in optical tweezer arrays as quantum sensors and as quantum processors in the same experimental setup. In the field of quantum sensing, a magnetic field resolution of 98(29) nT is demonstrated with a spatial resolution of a few micrometers. A sensitivity of the sensor of 25 µT/√Hz is achieved. Using the magnetic field measurement, one component of a quadrupole field with a range from −2µT to 7 µT is probed. The Ramsey spectroscopy used here is not limited to the measurement of magnetic fields, but allows the measurement of any field that causes a sufficient shift in the energy levels of the atoms. For the application of neutral atoms as a quantum processor, this work shows the demonstration of 1-qubit rotations, virtual-Z rotations and a restricted controlled NOT (CNOT) operation. The clock states in the hyperfine structure of individual rubidium atoms, known for their long coherence times, are used as qubit basis states. For the selected parameters, an inhomogeneous coherence time of T ∗ 2 = 340(26) µs is demonstrated with a perspective to a homogeneous coherence time of several milliseconds. Manipulations of the qubit states are performed on the basis of two-photon transitions. By varying the reference phase of an optical phaselocked loop, virtual-Z rotations on superpositions of these basis states are demonstrated. The interaction between the atoms is controlled using Rydberg states. The excitation of these states is studied in detail and typical limitations are addressed and partly associated with the generation of electrostatic fields. These fields are supposed to originate from rubidium atoms ab- and desorbed at the surfaces of the vacuum housing. To the author’s knowledge, an optical phase-locked loop is used for the first time to stabilize a laser on the transmitted light of a highly stable optical resonator with a Finesse larger than 30 000. The application of these operations to the atoms are explicitly designed to allow a scaling of the operations. A key feature is the controlled addressing of individual sites of the atom arrays, which is implemented for both the 1-qubit and the restricted CNOT operation. This represents a new approach in contrast to other quantum processors, which achieve the scaling of their quantum gates by moving the atoms in the optical registers. Addressing with light offers the prospect of an operation that is 100 times faster than the movement of the atoms allows.