Experimental triple-slit interference in a strongly driven V-type artificial atom

Dada, Adetunmise C.,Santana, Ted S.,Koutroumanis, Antonios,Ma, Yong,Park, Suk-In,Song, Jindong,Gerardot, Brian D. American Physical Society 2017 Physical Review B Vol.96 No.8

<P>Rabi oscillations of a two-level atom appear as a quantum interference effect between the amplitudes associated with atomic superpositions, in analogy with the classic double-slit experiment which manifests a sinusoidal interference pattern. By extension, through direct detection of time-resolved resonance fluorescence from a quantum-dot neutral exciton driven in the Rabi regime, we experimentally demonstrate triple-slit-type quantum interference via quantum erasure in a V-type three-level artificial atom. This result is of fundamental interest in the experimental studies of the properties of V-type three-level systems and may pave the way for further insight into their coherence properties as well as applications for quantum information schemes. It also suggests quantum dots as candidates for multipath-interference experiments for probing foundational concepts in quantum physics.</P>

Remarks on the Standard Model predictions for R(D) and R(D*)

Kim, C. S.,Lopez-Castro, G.,Tostado, S. L.,Vicente, A. American Physical Society 2017 Physical review. D Vol.95 No.1

<P>Semileptonic b -> c transitions, and in particular the ratios R(D-(*())) = Gamma(B -> D-(*())tau nu)/Gamma(B -> D-(*())l nu), can be used to test the universality of the weak interactions. In light of the recent discrepancies between the experimental measurements of these observables by the BABAR, Belle, and LHCb collaborations and the Standard Model predicted values, we study the robustness of the latter. Our analysis reveals that R(D) might be enhanced by lepton mass effects associated to the mostly unknown scalar form factor. In contrast, the Standard Model prediction for R(D*) is found to be more robust, because possible pollutions from B* contributions turn out to be negligibly small; this indicates that R(D) is a promising observable for searches of new physics.</P>

Plug-and-play measurement-device-independent quantum key distribution

Choi, Yujun,Kwon, Osung,Woo, Minki,Oh, Kyunghwan,Han, Sang-Wook,Kim, Yong-Su,Moon, Sung American Physical Society 2016 Physical Review A Vol.93 No.3

<P>Quantum key distribution (QKD) guarantees unconditional communication security based on the laws of quantum physics. However, practical QKD suffers from a number of quantum hackings due to the device imperfections. From the security standpoint, measurement-device-independent quantum key distribution (MDI-QKD) is in the limelight since it eliminates all the possible loopholes in detection. Due to active control units for mode matching between the photons from remote parties, however, the implementation of MDI-QKD is highly impractical. In this paper, we propose a method to resolve the mode matching problem while minimizing the use of active control units. By introducing the plug-and-play (P&P) concept into MDI-QKD, the indistinguishability in spectral and polarization modes between photons can naturally be guaranteed. We show the feasibility of P&P MDI-QKD with a proof-of-principle experiment.</P>

Phenomenology of dark matter in chiral U(1)X dark sector

Ko, P.,Nomura, Takaaki American Physical Society 2016 Physical Review D Vol.94 No.11

<P>We consider dark matter physics in a model for the dark sector with extra dark U(1)(X) gauge symmetry. The dark sector is composed of exotic fermions that are charged under both dark U(1)(X) and the standard model SU(3)(C) xU(1)(Y) gauge groups, as well as standard model singlet complex scalars Phi and X with nonzero U(1)(X) charge. In this model, there are two dark matter candidates-a scalar and a fermion-both of which are stabilized by accidental Z(2) symmetry. Their thermal relic density, and direct and indirect detection constraints are discussed in detail and we search for the parameter space of the model accommodating dark matter observations. We also discuss constraints from diphoton resonance searches associated with the scalar field which breaks the dark U(1)(X), in a way consistent with dark matter physics. In addition, implications for collider physics are discussed, focusing on the production cross section of the scalar boson.</P>

Light flavon signals at electron-photon colliders

Muramatsu, Yu,Nomura, Takaaki,Shimizu, Yusuke,Yokoya, Hiroshi American Physical Society 2018 Physical Review D Vol.97 No.1

<P>Flavor symmetries are useful to realize fermion flavor structures in the standard model (SM). In particular, the discrete A(4) symmetry is used to realize lepton flavor structures, and some scalars-called flavons-are introduced to break this symmetry. In many models, flavons are assumed to be much heavier than the electroweak scale. However, our previous work showed that a flavon mass around 100 GeV is allowed by experimental constraints in the A(4) symmetric model with a residual Z(3) symmetry. In this paper, we discuss collider searches for such a light flavon phi(T). We find that electron-photon collisions at the International Linear Collider have advantages for searching for these signals. In electron-photon collisions, flavons are produced as e(-)gamma -> l(phi T)(-) and decay into two charged leptons. Then, we analyze signals of the flavor-conserving final state tau(+)tau(-)e(-) and the flavor-violating final states tau(+)mu(-)mu(-) and mu(+)tau(-)tau(-) by carrying out numerical simulations. For the former final state, SM background can be strongly suppressed by imposing cuts on the invariant masses of final-state leptons. For the latter final states, SM background is extremely small, because in the SM there are no such flavor-violating final states. We then find that sufficient discovery significance can be obtained, even if flavons are heavier than the lower limits from flavor physics.</P>

Magnetic transitions in the chiral armchair-kagome system Mn2Sb2O7

Peets, Darren C.,Sim, Hasung,Choi, Seongil,Avdeev, Maxim,Lee, Seongsu,Kim, Su Jae,Kang, Hoju,Ahn, Docheon,Park, Je-Geun American Physical Society 2017 Physical Review B Vol.95 No.1

<P>The competition between interactions in frustrated magnets allows a wide variety of new ground states, often exhibiting emergent physics and unique excitations. Expanding the suite of lattices available for study enhances our chances of finding exotic physics. Mn2Sb2O7 forms in a chiral, kagome-based structure in which a fourth member is added to the kagome-plane triangles to form an armchair unit and link adjacent kagome planes. This structural motif may be viewed as intermediate between the triangles of the kagome network and the tetrahedra in the pyrochlore lattice. Mn2Sb2O7 exhibits two distinct magnetic phase transitions, at 11.1 and 14.2 K, at least one of which has a weak ferromagnetic component. The magnetic propagation vector does not change through the lower transition, suggesting a metamagnetic transition or a transition involving a multicomponent order parameter. Although previously reported in the P3(1)21 space group, Mn2Sb2O7 actually crystallizes in P2, which allows ferroelectricity, and we show clear evidence of magnetoelectric coupling indicative of multiferroic order. The quasi-two-dimensional 'armchair-kagome' lattice presents a promising platform for probing chiral magnetism and the effect of dimensionality in highly frustrated systems.</P>

Triton binding energy and neutron-deuteron scattering up to next-to-leading order in chiral effective field theory

Song, Young-Ho,Lazauskas, Rimantas,van Kolck, U. American Physical Society 2017 Physical Review C Vol.96 No.2

<P>Determination of the proper power-counting scheme is an important issue for the systematic application of Chiral Effective Field Theory in nuclear physics. We analyze the cutoff dependence of three-nucleon observables (the neutron-deuteron scattering lengths and the triton binding energy) at the leading and next-to-leading orders of a power counting that ensures order-by-order renormalization in the two-nucleon system. Our results confirm that, as usually assumed in the literature, three-body forces are not needed for renormalization of the three-nucleon system up to next-to-leading order.</P>

Universal metastability of the low-spin state in Co2+systems: Non-Mott type pressure-induced spin-state transition in CoCl2

Kim, Bongjae,Kim, Kyoo,Min, B. I. American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.11

We have investigated the pressure-induced spin-state transition in Co2+ systems in terms of a competition between Hund's exchange energy (J) and crystal-field splitting (Delta(CF)). First, we show the universal metastability of the low-spin state in octahedrally coordinated Co2+ systems. Then we present the strategy to search for a Co2+ system, for which the mechanism of spin-state and metal-insulator transitions is governed not by Mott physics but by J versus Delta(CF) physics. Using CoCl2 as a prototypical Co2+ system, we have demonstrated the pressure-induced spin-state transition from high-spin to low-spin, which is accompanied with insulator-to-metal and antiferromagnetic to half-metallic ferromagnetic transitions. Combined with the metastable character of Co2+ and the high compressibility nature of CoCl2, a transition pressure as low as 27 GPa can be identified on the basis of J versus Delta(CF) physics.

First observation of time variation in the solar-disk gamma-ray flux with Fermi

Ng, Kenny C. Y.,Beacom, John F.,Peter, Annika H. G.,Rott, Carsten American Physical Society 2016 Physical Review D Vol.94 No.2

<P>The solar disk is a bright gamma-ray source. Surprisingly, its flux is about 1 order of magnitude higher than predicted. As a first step toward understanding the physical origin of this discrepancy, we perform a new analysis in 1-100 GeV using 6 years of public Fermi-LAT data. Compared to the previous analysis by the Fermi Collaboration, which analyzed 1.5 years of data and detected the solar disk in 0.1-10 GeV, we find two new and significant results: (1) In the 1-10 GeV flux (detected at > 5 sigma), we discover a significant time variation that anticorrelates with solar activity, and (2) we detect gamma rays in 10-30 GeV at > 5 sigma and in 30-100 GeV at > 2 sigma. The time variation strongly indicates that solar-disk gamma rays are induced by cosmic rays and that solar atmospheric magnetic fields play an important role. Our results provide essential clues for understanding the underlying gamma-ray production processes, which may allow new probes of solar atmospheric magnetic fields, cosmic rays in the solar system, and possible new physics. Finally, we show that the Sun is a promising new target for ground-based TeV gamma-ray telescopes such as HAWC and LHAASO.</P>

Nonclassical-state generation in macroscopic systems via hybrid discrete-continuous quantum measurements

Milburn, T. J.,Kim, M. S.,Vanner, M. R. American Physical Society 2016 Physical Review A Vol.93 No.5

<P>Nonclassical-state generation is an important component throughout experimental quantum science for quantum information applications and probing the fundamentals of physics. Here, we investigate permutations of quantum nondemolition quadrature measurements and single quanta addition or subtraction to prepare quantum superposition states in bosonic systems. The performance of each permutation is quantified and compared using several different nonclassicality criteria including Wigner negativity, nonclassical depth, and optimal fidelity with a coherent-state superposition. We also compare the performance of our protocol using squeezing instead of a quadrature measurement and find that the purification provided by the quadrature measurement can significantly increase the nonclassicality generated. Our approach is ideally suited for implementation in light-matter systems such as quantum optomechanics and atomic spin ensembles, and offers considerable robustness to initial thermal occupation.</P>