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

Quantum mode filtering of non-Gaussian states for teleportation-based quantum information processing

We propose and demonstrate an effective mode-filtering technique of non-Gaussian states generated by photon-subtraction. More robust non-Gaussian states have been obtained by removing noisy low frequencies from the original mode spectrum. We show that non-Gaussian states preserve their non-classicality after quantum teleportation to a higher degree, when they have been mode-filtered. This is indicated by a stronger negativity $-0.033 \pm 0.005$ of the Wigner function at the origin, compared to $-0.018 \pm 0.007$ for states that have not been mode-filtered. This technique can be straightforwardly applied to various kinds of photon-subtraction protocols, and can be a key ingredient in a variety of applications of non-Gaussian states, especially teleportation-based protocols towards universal quantum information processing

Effect of bihemispheric transcranial direct current stimulation on distal upper limb function and corticospinal tract excitability in a patient with subacute stroke: a case study

IntroductionActivation of the unaffected hemisphere contributes to motor function recovery post stroke in patients with severe upper limb motor paralysis. Transcranial direct current stimulation (tDCS) has been used in stroke rehabilitation to increase the excitability of motor-related areas. tDCS has been reported to improve upper limb motor function; nonetheless, its effects on corticospinal tract excitability and muscle activity patterns during upper limb exercise remain unclear. Additionally, it is unclear whether simultaneously applied bihemispheric tDCS is more effective than anodal tDCS, which stimulates only one hemisphere. This study examined the effects of bihemispheric tDCS training on corticospinal tract excitability and muscle activity patterns during upper limb movements in a patient with subacute stroke.MethodsIn this single-case retrospective study, the Fugl–Meyer Assessment, Box and Block Test, electromyography, and intermuscular coherence measurement were performed. Intermuscular coherence was calculated at 15–30 Hz, which reflects corticospinal tract excitability.ResultsThe results indicated that bihemispheric tDCS improved the Fugl–Meyer Assessment, Box and Block Test, co-contraction, and intermuscular coherence results, as compared with anodal tDCS. Discussion: These results reveal that upper limb training with bihemispheric tDCS improves corticospinal tract excitability and muscle activity patterns in patients with subacute stroke

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