High-depth-resolution imaging of dispersive samples using quantum optical coherence tomography.

Quantum optical coherence tomography (QOCT) is a promising approach to overcome the degradation of the resolution in optical coherence tomography (OCT) due to dispersion. Here, we report on an experimental demonstration of QOCT imaging in the high-resolution regime. We achieved a depth resolution of 2.5 µm, which is the highest value for QOCT imaging, to the best of our knowledge. We show that the QOCT image of a dispersive material remains clear whereas the OCT image is drastically degraded.

Swept Source Lidar: simultaneous FMCW ranging and nonmechanical beam steering with a wideband swept source.

Light detection and ranging (lidar) has long been used in various applications. Solid-state beam steering mechanisms are needed for robust lidar systems. Here we propose and demonstrate a lidar scheme called "Swept Source Lidar" that allows us to perform frequency-modulated continuous-wave (FMCW) ranging and nonmechanical beam steering simultaneously. Wavelength dispersive elements provide angular beam steering, while a laser frequency is continuously swept by a wideband swept source over its whole tuning bandwidth. Employing a tunable vertical-cavity surface-emitting laser and a 1-axis mechanical beam scanner, three-dimensional point cloud data has been obtained. Swept Source Lidar systems can be flexibly combined with various beam steering elements to realize full solid-state FMCW lidar systems.

Mean-Field Scaling of the Superfluid to Mott Insulator Transition in a 2D Optical Superlattice.

The mean-field treatment of the Bose-Hubbard model predicts properties of lattice-trapped gases to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z. We test this scaling directly by comparing coherence properties of ^{87}Rb gases that are driven across the superfluid to Mott insulator transition within optical lattices of either the kagome (z=4) or the triangular (z=6) geometries. The coherent fraction measured for atoms in the kagome lattice is lower than for those in a triangular lattice with the same interaction and tunneling energies. A comparison of measurements from both lattices agrees quantitatively with the scaling prediction. We also study the response of the gas to a change in lattice geometry, and observe the dynamics as a strongly interacting kagome-lattice gas is suddenly "hole doped" by introducing the additional sites of the triangular lattice.

Observation of 1.2-GHz linewidth of zero-phonon-line in photoluminescence spectra of nitrogen vacancy centers in nanodiamonds using a Fabry-Perot interferometer.

Photoluminescence (PL) spectra of single nitrogen vacancy (NV) centers in 50-nm diamond nanocrystals at the zero-phonon line (ZPL) were directly observed using a Fabry-Perot interferometer at cryogenic temperatures. The narrowest linewidth of ZPL was 1.2 GHz (1.9 ± 0.7 GHz on average), comparable to ZPL linewidths in PL spectra reported for NV centers in pure bulk diamond. This observation is important to the application of NV centers for use in quantum communication and computation devices, and in nano-sensing.

Basilar Artery Occlusion Caused by Extracranial Vertebral Artery Dissection on Its Entry into the Transverse Foramen of the C6 Vertebra: Case Report.

Objective: Basilar artery occlusion (BAO) is an infrequent form of acute life-threatening stroke and may occur secondary to vertebral artery dissection (VAD). VAD, which occurs spontaneously and sometimes results from mechanical stress or blunt force trauma to the neck, sometimes occurs in the V1-V2 junction, but there are not many reported cases of those. Herein, we report a pictorially illustrative and clinically informative case of VAD in the V1-V2 junction following BAO. Case Presentation: The patient was a 27-year-old woman who was transferred to our hospital with abrupt severe unconsciousness. On admission, she presented with generalized convulsions and respiratory arrest, and pan-scan CT and CTA indicated BAO. We performed mechanical thrombectomy and achieved recanalization of the basilar artery, and she was diagnosed with BAO secondary to the right VAD at the entry of the C6 transverse foramen (V1-V2 junction). In hindsight, she had scapula and back pain before the onset. She recovered with a modified Rankin scale score of 3 after 90 days from the onset. Conclusion: VAD sometimes occurs at its entry into the transverse foramen of the C6 vertebra. In this case, VAD may be affected by minor trauma and potentially histological fragility due to the embryonic development process. Although BAO is sometimes difficult to diagnose because it presents with various symptoms, BAO secondary to VAD should be considered in cases of abrupt severe unconsciousness preceded by neck, scapula, or back pain in young and healthy persons.

Generation of broadband spontaneous parametric fluorescence using multiple bulk nonlinear crystals.

We propose a novel method for generating broadband spontaneous parametric fluorescence by using a set of bulk nonlinear crystals (NLCs). We also demonstrate this scheme experimentally. Our method employs a superposition of spontaneous parametric fluorescence spectra generated using multiple bulk NLCs. A typical bandwidth of 160 nm (73 THz) with a degenerate wavelength of 808 nm was achieved using two ß-barium-borate (BBO) crystals, whereas a typical bandwidth of 75 nm (34 THz) was realized using a single BBO crystal. We also observed coincidence counts of generated photon pairs in a non-collinear configuration. The bandwidth could be further broadened by increasing the number of NLCs. Our demonstration suggests that a set of four BBO crystals could realize a bandwidth of approximately 215 nm (100 THz). We also discuss the stability of Hong-Ou-Mandel two-photon interference between the parametric fluorescence generated by this scheme. Our simple scheme is easy to implement with conventional NLCs and does not require special devices.

Noncollinear parametric fluorescence by chirped quasi-phase matching for monocycle temporal entanglement.

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Opt. Express 98, 063602 (2007)] suggested using ultrabroad parametric fluorescenc generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In the Harris's original proposal, it is assumed that the photons are collinearly generated and then spatially separated by frequency filtering Here, we alternatively propose using noncollinearly generated SPDC. In our numerical calculation, to achieve 1.2 cycle temporal correlation for a 532 nm pump laser, only 10% -chirped device is sufficien when noncollinear condition is applied, while a largely chirped (50%) device is required in collinear condition. We also experimentally demonstrate an octave-spanning (790-1610 nm) noncollinear parametric fluorescenc from a 10% chirped MgSLT crystal using both a superconducting nanowire single-photon detector and photomultiplier tube as photon detectors. The observed SPDC bandwidth is 194 THz, which is the largest width achieved to date for a chirped QPM device. From this experimental result, our numerical analysis predicts that the bi-photon can be compressed to 1.2 cycles with appropriate phase compensation.

Spinal Epidural Hematoma Due to Venous Congestion Caused by Nutcracker Syndrome.

The causes of spinal epidural hematoma (SEH) have been attributed to coagulopathy, trauma, vascular anomalies, and so forth. The incidence of vascular anomalies shown by digital subtraction angiography has been reported to be 15%, and most cases have been reported to be spinal epidural arteriovenous fistulae. SEH has rarely been caused by venous congestion. We report a case of SEH in a 78-year-old male who presented to our emergency department with sudden-onset back pain, followed by complete paraplegia with bladder and rectal disturbance. Magnetic resonance imaging revealed a dorsally placed extradural hematoma extending from T10 to L1. An urgent laminectomy from T11 to L2 was performed. Computed tomography angiography (CTA) performed 1 week after the operation showed compression of the left renal vein between the aorta and superior mesenteric artery with dilation of the surrounding veins, including the spinal epidural venous plexus, at the same level as the hematoma. This was diagnosed as Nutcracker syndrome (NCS), which was consistent as a cause of SEH. The patient's symptoms gradually improved, and after 6 months, he regained normal strength in his lower extremities, but bladder and rectal disturbance remained and required intermittent self-catheterization. We chose conservative treatment for NCS, and SEH did not recur until the patient died of a cause unrelated to SEH or NCS. SEH could occur secondary to venous congestion including NCS. We emphasize the importance of investigating venous return to evaluate the etiology of SEH, which can be clearly visualized using CTA.

0.54 µm resolution two-photon interference with dispersion cancellation for quantum optical coherence tomography.

Quantum information technologies harness the intrinsic nature of quantum theory to beat the limitations of the classical methods for information processing and communication. Recently, the application of quantum features to metrology has attracted much attention. Quantum optical coherence tomography (QOCT), which utilizes two-photon interference between entangled photon pairs, is a promising approach to overcome the problem with optical coherence tomography (OCT): As the resolution of OCT becomes higher, degradation of the resolution due to dispersion within the medium becomes more critical. Here we report on the realization of 0.54 µm resolution two-photon interference, which surpasses the current record resolution 0.75 µm of low-coherence interference for OCT. In addition, the resolution for QOCT showed almost no change against the dispersion of a 1 mm thickness of water inserted in the optical path, whereas the resolution for OCT dramatically degrades. For this experiment, a highly-efficient chirped quasi-phase-matched lithium tantalate device was developed using a novel 'nano-electrode-poling' technique. The results presented here represent a breakthrough for the realization of quantum protocols, including QOCT, quantum clock synchronization, and more. Our work will open up possibilities for medical and biological applications.