Hee Su Park

Three-photon N00N states generated by photon subtraction from double photon pairs

We describe an experimental demonstration of a novel three-photon N00N state generation scheme using a single source of photons based on spontaneous parametric down-conversion (SPDC). The three-photon entangled state is generated when a photon is subtracted from a double pair of photons and detected by a heralding counter. Interference fringes measured with an emulated three-photon detector reveal the three-photon de Broglie wavelength and exhibit visibility > 70% without background subtraction.

International key comparison of measurements of neutron source emission rate (1999–2005): CCRI(III)-K9.AmBe

Section III (neutron measurements) of the Comite Consultatif des Rayonnements Ionisants, CCRI, conducted a key comparison of primary measurements of the neutron emission rate of an 241 Am-Be(α,n) radionuclide source. A single 241 Am-Be(α,n) source was circulated to all the participants between 1999 and 2005. Eight laboratories participated – the CIAE (China), CMI (Czech Republic), KRISS (Republic of Korea), LNMRI (Brazil), LNE-LNHB (France), NIST (USA), NPL (UK), and the VNIIM (Russian Federation) – with the NPL making their measurements at the start and repeating them near the end of the exercise to verify the stability of the source. Each laboratory reported the emission rate into 4π sr together with a detailed uncertainty budget. All participants used the manganese bath technique, with the VNIIM also making measurements using an associated particle technique. The CMI, KRISS, VNIIM, and later the NPL, also measured the anisotropy of the source although this was not a formal part of the comparison. The first draft report was released in May 2006 and having been discussed and modified by the participants and subsequently reviewed by the CCRI(III), the present paper is now the final report of the comparison.

Generation of super-resolution atomic state density distribution based on temporally-cascaded multiple light exposures.

We propose a novel approach to optical generation of superresolution atomic state density distribution based on interaction between Lambda- type atoms and temporally-cascaded driving fields. The scheme effectively inscribes multiplication of optical intensity profiles on atomic state density distribution, which can produce arbitrary patterns beyond the diffraction limit. The degree of resolution enhancement can be increased, not depending on the intrinsic nonlinearity of the photographic medium or the number of simultaneously interacting fields unlike the previous schemes. Procedures for drawing arbitrary two-dimensional patterns and effects of atomic state decoherence are described.

Observation of Young’s double-slit interference with the three-photon N00N state

We report the first experimental observation of a three-photon N00N state exhibiting Youngs double-slit type spatial quantum interference. Compared to a single-photon state, the three-photon entangled state generates interference fringes that are three times denser.

Experimental realization of a four-photon seven-qubit graph state for one-way quantum computation

We propose and demonstrate the scaling up of photonic graph states through path qubit fusion. Two path qubits from separate two-photon four-qubit states are fused to generate a two-dimensional seven-qubit graph state composed of polarization and path qubits. Genuine seven-qubit entanglement is verified by evaluating the witness operator. Six qubits from the graph state are used to demonstrate the Deutsch-Jozsa algorithm for general two-bit functions with a success probability greater than 90%.

Continuous-wave 532 nm pumped MgO:PPLN optical parametric oscillator with external power regulation and spatial mode filtering

We report a continuous-wave (CW) optical parametric oscillator (OPO) based on a MgO-doped periodically poled LiNbO(3) (MgO:PPLN) crystal. The 532 nm pump generates coherent radiation that is tunable from 800 to 920 nm for the signal and from 1250 to 1580 nm for the idler, respectively. The OPO output power exhibits a slowly varying instability that we attribute to a thermal effect induced by the pump. This instability is truncated by means of a low-pass servo that includes a single-mode fiber that filters the beam into a single spatial mode. The resulting output characteristics are promising for radiometric applications in the near infrared including most fiber-optic communication bands.

Multi-core fiber interferometer using spatial light modulators for measurement of the inter-core group index differences

We demonstrate an experimental technique to generate and measure arbitrary superpositions of core modes in a multi-core fiber. Two spatial light modulators couple the fundamental mode of a single-mode fiber with multiple-core modes of the MCF to constitute a Mach-Zehnder-type multi-path interferometer. The phase tunability of each path is verified by comparing two-, three-, and four-path interference patterns with the theory. Interference fringes in the wavelength domain estimates the inter-core group index differences with a resolution of 10(-5) using a fiber length of 1 m.

Acousto-optic resonant coupling of three spatial modes in an optical fiber.

A fiber-optic analogue to an externally driven three-level quantum state is demonstrated by acousto-optic coupling of the spatial modes in a few-mode fiber. Under the condition analogous to electromagnetically induced transparency, a narrow-bandwidth transmission within an absorption band for the fundamental mode is demonstrated. The presented structure is an efficient converter between the fundamental mode and the higher-order modes that cannot be easily addressed by previous techniques, therefore can play a significant role in the next-generation space-division multiplexing communications as an arbitrarily mode-selectable router.

Two-photon four-qubit cluster state generation based on a polarization-entangled photon pair

We propose and experimentally demonstrate a two-photon four-qubit cluster state generator using linear optics and a single polarization-entangled photon-pair source based on spontaneous parametric down-conversion (SPDC). Our novel scheme provides greater design flexibility compared to previous schemes that rely on hyperentanglement.

Experimental direct estimation of nonlinear functionals of photonic quantum states via interferometry with a controlled-swap operation

We propose a multi-photon interferometer with a generalized C-SWAP operation that can estimate Tr[ρ(1)ρ(2)···ρ(n)], a nonlinear functional of n photonic density matrices. The scheme is demonstrated for three single-photon states whose overlap is experimentally measured as the interference visibility of a control qubit encoded into photonic paths. The validity of this method is verified by comparing the visibility with the results of Hong-Ou-Mandel experiments.