Four-photon State Research Articles

Experimental observation of four-photon entanglement from parametric down-conversion.

We observe polarization entanglement between four photons produced from a single down-conversion source. The nonclassical correlations between the measurement results violate a generalized Bell inequality for four qubits. The characteristic properties and its easy generation with high interferometric contrast make the observed four-photon state well suited for implementing advanced quantum communication schemes such as multiparty quantum key distribution, secret sharing, and telecloning.

Scheme for fourfold de Broglie wavelength reduction of a multi-photon wavepacket

Twofold reduced de Broglie wavelengths have been observed in two-photon interference experiments. With present technology it should be possible to observe a fourfold reduction when using a four-photon state from spontaneous parametric down-conversion. It is proposed to use a Mach–Zehnder set-up, which shows boson enhancement at the input beamsplitter and thus allows us to circumvent fourth-order non-linearities which would be necessary otherwise. The fourfold decrease in the observed de Broglie wavelength with perfect visibility is in principle achievable. This constitutes a reduction of the observed de Broglie wavelength below the wavelength of the generating source.

Experimental violation of a spin-1 bell inequality using maximally entangled four-photon states.

We demonstrate the experimental violation of a spin-1 Bell inequality. The spin-1 inequality is based on the Clauser, Horne, Shimony, and Holt formalism. For entangled spin-1 particles, the maximum quantum-mechanical prediction is 2.55 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27+/-0.02 using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.

Practical scheme for entanglement concentration

We present a realistic purification scheme for pure non-maximally entangled states. In the scheme, Alice and Bob at two distant parties first start with two shared but less entangled photon pairs to produce a conditional four-photon GHZ state, then perform a 45-degree polarization measurement onto one of the two photons at each party such that the remaining two photons are projected onto a maximally entangled state.

Observation of Four-Photon Interference with a Beam Splitter by Pulsed Parametric Down-Conversion

When four photons arrive at a beam splitter, two from each side, a four-photon, six-path interference effect occurs to yield a sixfold enhancement of the probability for all four photons to exit together from the beam splitter. We produce the four-photon state by using the stimulated emission process in a pulsed parametric down-conversion and measure the probability for all four photons to exit from one side of the beam splitter. The observed enhancement factor is in good agreement with a multimode treatment of pulsed down-conversion.

Generation of entangled four-photon states by parametric down-conversion

Pairs of photons are commonly generated in an entangled state by parametric down-conversion of an ultraviolet pump beam in a nonlinear crystal. We show how this process can be extended to generate entangled four-photon states from two pump photons by using two non-collinear pump beams.

Generation of entangled four-photon states by parametric down-conversion

Abstract Pairs of photons are commonly generated in an entangled state by parametric down-conversion of an ultraviolet pump beam in a nonlinear crystal. We show how this process can be extended to generate entangled four-photon states from two pump photons by using two non-collinear pump beams.

Generation of four-photon coherent states in dispersive cavity QED.

I discuss the generation of certain kinds of four-photon coherent states in the context of dispersive cavity QED. These states, eigenstates of fourth power of the photon annihilation operator, may be expressed as various superpositions of four coherent states symmetrically located on a circle in phase space. I also point out that for low amplitude initial coherent states, number states containing one, two, or three photons can be produced in the cavity. The decay of these states can be monitored by doing parity measurements on the field from which the lifetime of a number state can be obtained. \textcopyright{} 1996 The American Physical Society.

Four-photon Coherent States

Abstract We present a detailed discussion of a type of four-photon coherent state defined as right eigenstates of the operator â 4 where â is the usual annihilation operator. There are actually four sets of states that need to be considered, namely those containing as the lowest number states ¦0>, ¦1>, ¦2>, or ¦3>. These correspond to the possible unique superpositions of the ordinary coherent states ¦±α> and ¦±iα>. We discuss the nonclassical properties of these states such as photon antibunching and squeezing. The usual second order squeezing does not exist for these states but higher order squeezing and square field amplitude squeezing do exist. Also discussed are the quasiprobability distributions, namely the P-function, the Q-function and the Wigner function. Finally, a method of generating these states based on the competition between a four-photon parametric process and incoherent losses from four-photon absorption is presented.

A study of the three- and four-photon final states produced in e +e − annihilation at [formula omitted

The reactions e +e −→γγγ and e +e −→γγγγ have been studied at center-of-mass energies between 35 and 46.8 GeV with an integrated luninosity of about 130 pb −1accumulated with the CELLO detector at PETRA. The measurements are compared to QED calculations up to third and fourth orders of perturbation theory. Excellent agreement is observed.

Tests of quantum electrodynamics with two-, three-, and four-photon final states from e+e- annihilation at sqrt s =29 GeV.

High-precision measurements of electron-positron annihilation into final states of two, three, and four photons are presented. The data were obtained with the MAC detector at the PEP storage ring of the Stanford Linear Accelerator Center, at a center-of-mass energy of 29 GeV. The measured e+e−→γγ differential cross section is used to test the validity of quantum electrodynamics (QED) in this energy range; it agrees well with QED, and the limit on cutoff parameters for the electron propagator is Λ>66 GeV. The measurement of e+e−→γγγ is used to test the QED calculations of order α3 and to search for anomalies that would indicate the existence of new particles; the agreement with QED is excellent and no anomalies are found. Two events from the reaction e+e−→γγγγ are found, in agreement with the QED prediction.Received 23 June 1986DOI:https://doi.org/10.1103/PhysRevD.35.1©1987 American Physical Society

Production of π0π0 and π0η in photon-photon collisions

We investigate the four-photon final state produced in γγ colissions. In the π 0 π 0 channel we observe f(1270) production with predominantly helicity 2 and measure a partial width Γ γγ 2.9 +0.6 −0.4 ± keV (independent of assumptions on the helicity). We observe A 2(1310) production in the π 0 η channel and find a partial width Γ γγ = 0.77 ± 0.18 ± 0.27 KeV (assuming helicity 2). We give an upper limit for f ≈ ηη.