Magnetic levitation and harmonic trapping of soft ferromagnets for macroscopic quantum mechanics

We propose a system for passive magnetic levitation and three-dimensional harmonic trapping of soft ferromagnets. Our protocol utilizes the magnetic field gradient for vertical trapping, and the finite size effect of the Meissner effect for horizontal trapping. We provide numerical and analytical estimations of possible mechanical dissipations to show that our system allows high mechanical Q-factors above $Q > 10^8$, and quantum control of the levitated object is within reach of current technologies. The utilization of soft ferromagnet's internal collective spin excitation may allow quantum mechanical phenomena with particles as large as the sub-millimeter-scale.Comment: 10 pages, 9 figure

Analog of the Clauser-Horne-Shimony-Holt inequality for steering

The Clauser-Horne-Shimony-Holt (CHSH) inequality (and its permutations), are necessary and sufficient criteria for Bell nonlocality in the simplest Bell-nonlocality scenario: 2 parties, 2 measurements per party and 2 outcomes per measurement. Here we derive an inequality for EPR-steering that is an analogue of the CHSH, in that it is necessary and sufficient in this same scenario. However, since in the case of steering the device at Bob's site must be specified (as opposed to the Bell case in which it is a black box), the scenario we consider is that where Alice performs two (black-box) dichotomic measurements, and Bob performs two mutually unbiased qubit measurements. We show that this inequality is strictly weaker than the CHSH, as expected, and use it to decide whether a recent experiment [Phys. Rev. Lett. 110, 130401 (2013).] involving a single-photon split between two parties has demonstrated EPR-steering.Comment: Expanded v2, new results, new figure. 9 pages, 2 figure

Deterministic quantum teleportation of photonic quantum bits by a hybrid technique

Quantum teleportation allows for the transfer of arbitrary, in principle, unknown quantum states from a sender to a spatially distant receiver, who share an entangled state and can communicate classically. It is the essence of many sophisticated protocols for quantum communication and computation. In order to realize flying qubits in these schemes, photons are an optimal choice, however, teleporting a photonic qubit has been limited due to experimental inefficiencies and restrictions. Major disadvantages have been the fundamentally probabilistic nature of linear-optics Bell measurements as well as the need for either destroying the teleported qubit or attenuating the input qubit when the detectors do not resolve photon numbers. Here we experimentally realize fully deterministic, unconditional quantum teleportation of photonic qubits. The key element is to make use of a "hybrid" technique: continuous-variable (CV) teleportation of a discrete-variable, photonic qubit. By optimally tuning the receiver's feedforward gain, the CV teleporter acts as a pure loss channel, while the input dual-rail encoded qubit, based on a single photon, represents a quantum error detection code against amplitude damping and hence remains completely intact for most teleportation events. This allows for a faithful qubit transfer even with imperfect CV entangled states: the overall transfer fidelities range from 0.79 to 0.82 for four distinct qubits, all of them exceeding the classical limit of teleportation. Furthermore, even for a relatively low level of the entanglement, qubits are teleported much more efficiently than in previous experiments, albeit post-selectively (taking into account only the qubit subspaces), with a fidelity comparable to the previously reported values

連続量離散量融合型量子情報処理の研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 古澤 明, 東京大学教授 香取 秀俊, 東京大学教授 中村 泰信, 東京大学教授 小芦 雅斗, 東京大学教授 湯本 潤司University of Tokyo(東京大学

Generation and Eight-port Homodyne Characterization of Time-bin Qubits for Continuous-variable Quantum Information Processing

We experimentally generate arbitrary time-bin qubits using continuous-wave light. The advantage unique to our qubit is its compatibility with deterministic continuous-variable quantum information processing. This compatibility comes from its optical coherence with continuous waves, well-defined spatio-temporal mode, and frequency spectrum within the operational bandwidth of the current continuous-variable technology. We also demonstrate an efficient scheme to characterize time-bin qubits via eight-port homodyne measurement. This enables the complete characterization of the qubits as two-mode states, as well as a flexible analysis equivalent to the conventional scheme based on a Mach-Zehnder interferometer and photon-detection

Rapid, metal-free and aqueous synthesis of imidazo[1,2-a]pyridine under ambient conditions

A novel, rapid and efficient route to imidazo[1,2-a]pyridines under ambient, aqueous and metal-free conditions is reported. The NaOH-promoted cycloisomerisations of N-propargylpyridiniums give quantitative yield in a few minutes (10 g scale). A comparison of common green metrics to current routes showed clear improvements, with at least a one order of magnitude increase in space-time-yield