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Elements of Quantum Electronics
Published in Michael Olorunfunmi Kolawole, Electronics, 2020
Qubit is the fundamental carrier of quantum information, which may take many physical forms, such as trapped ions, neutral atoms, photons, superconducting devices, to name a few. Classical computation and classical information work by manipulating binary digital bits that exist in one of two states: zero “0,” or one “1,” and there is nothing in between. A qubit state is not restricted to these two states: “0” {green} and “1” {yellow} but can also exist in a superposition of both states, depicted as {red} in Figure 9.1.
A survey on quantum positioning system
Published in International Journal of Modelling and Simulation, 2021
Shiqi Duan, Shuang Cong, Yuanyuan Song
A considerable number of researchers have attempted to achieve entangled states of two or even more atoms in trapped ion systems. The two advantages of using the ion trap scheme to prepare entanglement state are (1) because the ions are trapped in a high vacuum environment, they are almost in isolation without interference, and have a long time of decoherence; (2) the preparation of initial state and the measurement of quantum state have extremely high fidelity and efficiency. These advantages also provide very favorable conditions for quantum computing and quantum information processing. The disadvantage of this scheme is that it is not easy to cool the ion motion to the vibrating ground state. In 1998, the NIST team in America prepared the internal states of two ions in both singlet and triplet entanglement states, and this state is quite close to the maximum entangled Bell state [72]. One disadvantage of this state preparation is that once the ratio of the two rabbinic frequencies is determined, it cannot be changed during the experiment. Therefore, the maximum entangled state of two particles (EPR) cannot be produced. In the same year, Steinbach proposed a scheme to prepare the maximum entangled state of ions by using a series of carrier frequency pulses and red sideband pulses that resonate with ions to successively manipulate the evolution of states. This method has been successfully used by NIST’s ion trap group to prepare the quantum state of the external motion of ions [73]. In 1999, Solano proposed another scheme that could prepare any of the four Bell states, and this method can also be applied to the acquisition of multiparticle entangled states [74]. Meanwhile, Klaus prepared the maximum entangled state by irradiated ions simultaneously with two beams of light [75]. In 2016, Justin verified the spin-squeezed state entanglement characteristics of 219 ions and observed the spectral entanglement of dB directly, which has some significance for studying the spin correlation of a quantum system [76].
Precise positioning of an ion in an integrated Paul trap-cavity system using radiofrequency signals
Published in Journal of Modern Optics, 2018
Ezra Kassa, Hiroki Takahashi, Costas Christoforou, Matthias Keller
The field of atomic physics has advanced greatly since the advent of ion traps which confine ions for unprecedented durations without utilising the internal states of the ions. Because ion traps offer unparalleled levels of control over the ions’ mechanical and internal degrees of freedom, many experiments have sought to combine them with optical cavities for enhanced atom-light interactions. As a result, there have been a number of significant experiments: single photons were generated on demand [1], cavity sideband cooling was performed on single ions [2], super-radiance was observed with the collective coupling of coulomb crystals [3], tunable ion-photon entanglement has been demonstrated [4], multiple ions have been deterministically coupled to a cavity [5]. The combination of ion traps with optical cavities is also considered to be one of the most promising avenues for advances in quantum information processing. Whilst there has been remarkable progress in the preparation, gate operation and readout of qubits [6,7], to date, these implementations have been limited to small scales, with 14 being the largest number of qubits entangled [8]. Presently, challenges in the physical implementations of large quantum systems pose the greatest difficulty in advancing experimental quantum information science. Among the proposed solutions to tackle the scalability problem (e.g. [9–12]), distributed quantum information processing based on photonic links is the most promising. Notably, modular approaches using trapped ions as stationary qubits have attracted significant interest. However, so far, optically heralded entanglement with remote trapped ions has only been demonstrated using high numerical aperture lenses for the collection of photons, a method which suffers from low efficiencies in the entanglement generation[13,14]. Placing the ions in an optical cavity, this efficiency can be greatly enhanced. Further, by reducing the cavity mode volume, one can enhance the ion-cavity coupling and, subsequently, the efficiency of operations. To this end, fiber-based Fabry-Pérot cavities (FFPCs) have been combined with ion traps [15–17]. In such ion trap-cavity systems, the optimal positioning of the ion with respect to the cavity mode is of vital importance. In the previously demonstrated designs of ion traps combining FFPCs [15–17], the FFPCs were mechanically translated to optimise the overlap between the ion and the cavity mode. In addition to the need for a three-dimensional positioning system which tends to be bulky and expensive, the movable cavities affect the trapping field and shift the geometrical center of the trap as they are moved. This adds complexity to the trapping and optimisation of the ion-cavity coupling.