In this proceedings, we have summarized the main results of Ref. [1], where we illustrated that an entangled qubit system involving $N$ ions can enhance the excitation rate by a factor of $N^2$ in the framework of a linear ion trap system. Our results highlight the importance of quantum entanglement for new physics search.
In this proceedings, we have summarized the main results of Ref. [1], where we illustrated that an entangled qubit system involving N ions can enhance the excitation rate by a factor of N2 in the framework of a linear ion trap system. Our results highlight the importance of quantum entanglement for new physics search.
An introductory review is provided for those who are interested in exploring applications of qubits and other quantum excitations to the detection of dark matter (and any other physics beyond the Standard Model). Topics covered include the fundamental properties of qubits, the excitation mechanism of qubits due to the electric field induced by dark matter (with attention to the effects of the coherence of dark matter), the dynamics of coupled qubit-cavity systems modeled by the Jaynes-Cummings framework, and the influence of noise and decoherence (especially Markovian noise described by the Lindblad equation). In addition, the article introduces essential concepts in quantum sensing, including the operator-sum representation and positive operator-valued measures, the Cramér-Rao bound, the standard quantum limit and the Heisenberg limit, and the potential enhancement of sensitivity to dark matter achievable with entangled states. Throughout, these topics are discussed with particular emphasis on their application to the detection of wave-like dark matter.
Quantum sensing with qubits has advanced fundamental physics searches, but higher dimensional systems offer untapped potential. We present a universal qutrit framework that yields a sequence-independent fourfold increase in quantum Fisher information and a twofold gain in sensitivity. In ultralight dark matter searches, spin-1 NV-center qutrits can enhance the axion-electron coupling reach by an order of magnitude beyond qubits. This principle applies broadly to multilevel quantum systems including superconducting, neutral atom and trapped-ion qutrits, establishing higher dimensional sensing as a powerful tool for probing new physics.
Combining optical cavities with trapped atomic ions is a powerful tool to investigate the interaction of light with matter on the most fundamental scale: a single atom with a single particle of light. Recent advances have not only demonstrated the emission of single photons, ion-photon entanglement and ion-ion entanglement but paved the way to use these systems in modern quantum technologies. Ion-cavity systems are now one of the most promising technologies for realising a scalable quantum computer and quantum networks. While the integration of optical cavities and ion traps is challenging, new techniques and technologies made it possible to demonstrate important building blocks for such systems.
Since the development of quantum mechanics almost a century ago, there has been considerable controversy over the interpretations and predictions of quantum theory. Owing to the counterintuitive predictions of quantum mechanics, Einstein himself even wondered if this theory should be considered complete. While these questions have troubled many physicists over the past century, the development of the new field of quantum information science and the applications that may result from large scale quantum systems have brought many of these fundamental questions of quantum mechanics to the mainstream of not only theoretical but also experimental physics. This thesis deals with a system at the heart of these questions - the first demonstration of quantum entanglement of two individual massive particles at a distance. I describe a theoretical and experimental framework for entanglement of two particles using trapped atomic ions. Trapped ions are among the most attractive systems for scalable quantum information protocols because they can be well isolated from the environment and manipulated easily with lasers. Using our trapped ion system, I show the first explicit demonstration of quantum entanglement between matter and light using a single ion and its single emitted photon. Further, by combining two such ion-photon entangled systems, I demonstrate the entanglement of two remotely located ions. These entanglement protocols, together with the recent developments of trapped ion quantum computing, can be used to create a platform for a scalable quantum information network, and perhaps confront some of the strangest features of quantum mechanics.
We propose an array of Ramsey-type interferometers using N superposition states, (∣0⟩+∣1⟩)⊗N, as a sensor to detect wave-like dark matter. After exposure to the dark matter wave, which induces coherent qubit transitions, the signal is the imbalance between the numbers of 0 and 1 outcomes. The signal-to-noise ratio in this scheme is proportional to Nα2, where α is the coupling of dark matter to the qubits, and thus the sensitivity to the coupling scales as δα∼1/N. For comparison, in the detection scheme based on the Rabi-type transition, ∣0⟩→∣1⟩, this scaling is achieved only when N highly entangled qubits are used. Since the Ramsey-type measurement does not require entangled states, one can consider much larger N by simply placing a large number of qubits within the de Broglie wavelength of the dark matter. We demonstrate that, using trapped-ion qubits in linear Paul traps as the sensor, the projected sensitivity to the coupling matches or surpasses existing laboratory, astrophysical, and cosmological bounds for N≳106-108. We also evaluate its sensitivity to high-frequency gravitational waves. Our general framework should, in principle, be useful for other quantum sensing platforms.
This work investigates the use of linear Paul traps as quantum sensors for detecting megahertz gravitational waves. Single-ion configurations exploit graviton-photon conversion in the presence of external magnetic fields, while two-ion systems use relative-motion excitations, which do not require magnets, to distinguish gravitational waves from axion dark matter. Furthermore, we show that entanglement of N vibrational qubits enhances the signal probability by a factor of N 2 , improving sensitivity beyond the standard quantum limit.