Two-photon Interference Experiment Research Articles

진동수가 서로 다른 얽힘상태 광자쌍의 4차 간섭

매개하향변환과정에서 동시에 발생한 서로 다른 진동수의 광자쌍을 이용한 4차 간섭실험에서 비고전적인 맥놀이 효과를 측정하였다. 각진동수가 각각 <TEX>$\omega1$</TEX>과 <TEX>$\omega2$</TEX>인 광자쌍을 빔분할기에서 중첩시키고, 빔분할기의 두 출구에 놓인 두 검출기로 동시계수 할 때, 두 광자가 빔분할기에 도달하는 시간 간격에 따라 cos(<TEX>$\omega1$</TEX>-<TEX>$\omega2$</TEX>)의 함수로 동시계수의 변화를 나타내었다. 두 광자의 파장 차이가 41㎚일 때 측정된 맥놀이 진동수 (<TEX>$\omega1$</TEX>-<TEX>$\omega2$</TEX>)/2<TEX>$\pi$</TEX>는 0.29<TEX>${\times}10^{14}$</TEX>㎐이었고, 진동수 차이에 해당하는 두 광자의 시간간격은 34.82fs로 측정되었다. One of the nonclassical effects in two-photon interference experiments, spatial quantum beating, is observed in fourth-order interference with pairs of photons produced by a spontaneous parametric down-conversion process. When photon pairs in different frequencies <TEX>$\omega1$</TEX> and <TEX>$\omega2$</TEX> are mixed together, and directed to two detectors, the coincidence counts exhibit a cosine modulation with difference frequency | <TEX>$\omega1$</TEX>- <TEX>$\omega2$</TEX>|. The measured coincidence counts turned out to have an interference pattern with periodicity of 10.45 ㎛ in position or 34.82fs in time delay, which corresponds to the period 2<TEX>$\pi$</TEX>/| <TEX>$\omega1$</TEX>- <TEX>$\omega2$</TEX>| for the beat frequency of 0.29<TEX>${\times}10^{14}$</TEX>Hz.

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.

Quantum interference and diffraction of parametric down-converted biphotons

We present two-photon diffraction and interference experiments utilizing parametric down-converted photon pairs (biphotons) and a transmission grating. The biphoton exhibits a diffraction-interference pattern equivalent to an effective single particle with half wavelength of the constituent photons.

New High-Efficiency Source of Photon Pairs for Engineering Quantum Entanglement

We constructed an efficient source of photon pairs using a waveguide-type nonlinear device and performed a two-photon interference experiment with an unbalanced Michelson interferometer. As the interferometer has two arms of different lengths, photons from the short arm arrive at the detector earlier than those from the long arm. We find that the arrival time difference (Delta L/c) and the time window of the coincidence counter (Delta T) are important parameters which determine the boundary between the classical and quantum regimes. Fringes of high visibility ( 80% +/- 10%) were observed when Delta T < Delta L/c. This result is explained only by quantum theory and is clear evidence for quantum entanglement of the interferometer's optical paths.

Bell Theorem for Some Quantum Interferometric Experiments

We discuss the problem of existence of local and realistic models for some of the classic two-photon interference experiments. These include the early PDC experiments, as well as the most recent ones involving entanglement swapping.

Two-photon double-slit interference experiment

We report a two-photon double-slit interference experiment. Two correlated photons, generated by spontaneous parametric downconversion and traveling in different directions, are made to pass through a double slit in such a way that the path of one photon can be identified with that of the other photon. No single-photon interference pattern is observed even if the path is not actually identified, but a spatial interference pattern appears in the joint detection counting rates of the photon pairs. It can easily be shown that these nonlocal phenomena cannot be exhibited by any kind of classical field.

What we can learn about single photons in a two-photon interference experiment

What we can learn about single photons in a two-photon interference experiment

Two-photon geometrical phase

An advanced wave model is applied to a two-photon interference experiment to show that the observed interference effect is due to the geometrical phase of a two-photon state produced in spontaneous parametric down-conversion. The polarization state of the signal-idler pair is changed adiabatically so that the ``loop'' on the Poincar\'e sphere is opened in the signal channel and closed in the idler channel. Therefore, we observed an essentially nonlocal geometrical phase, shared by the entangled photon pair, or a biphoton.

Nonlocal correlation in the realization of a quantum eraser

It is pointed out that a recent two-photon interference experiment [Z.Y. Ou et al., Phys. Rev. A 41 (1990) 566] can be modified to realize an optimal quantum eraser. A detailed analysis shows that the nonlocal correlation is the key for a delayed choice experiment in the demonstration of a quantum eraser.

Photon tunneling through absorbing dielectric barriers

Using a recently developed formalism of quantization of radiation in the presence of absorbing dielectric bodies, the problem of photon tunneling through absorbing barriers is studied. The multilayer barriers are described in terms of multistep complex permittivities in the frequency domain which satisfy the Kramers-Kronig relations. From the resulting input-output relations it is shown that losses in the layers may considerably change the photon tunneling times observed in two-photon interference experiments. It is further shown that for sufficiently large numbers of layers interference fringes are observed that cannot be related to a single traversal time.

Postselection-free energy-time entanglement.

We report a two-photon interference experiment that realizes a postselection-free test of Bell's inequality based on energy-time entanglement. In contrast with all previous experiments of this type, the employed entangled states are obtained without the use of a beam splitter or a short coincidence window to "throw away" unwanted amplitudes. A (95.0\ifmmode\pm\else\textpm\fi{}1.4)% interference fringe visibility is observed, implying a strong violation of the Bell inequality. The scheme is very compact and has demonstrated excellent stability, suggesting that it may be useful, for example, in practical quantum cryptography.

Geometric phases in two-photon interference experiments.

Photon pairs produced by type-I and type-II parametric down-conversion are passed through a Michelson interferometer. Two quarter-wave plates in one arm of the interferometer allow variation of the polarization state of the photons. We investigate experimentally the geometric phase or Pancharatnam phase acquired by single photons and photon pairs dependent on the solid angle that is subtended by the circuit that represents the varying state of polarization on the Poincar\'e sphere. It is found that the geometric phase acquired by the pair depends on the initial polarization state of the two photons. If both photons are in equal states of linear polarization, we observe a doubling of the geometric phase compared to single photons; in the case of orthogonal states of linear polarization, the geometric phase is completely canceled. Our results show the role of Pancharatnam's phase in nonclassical two-photon interference phenomena and the interplay between the geometric phase and the dynamical phase in these phenomena.

Reinterpretation of two-photon interference experiment using advanced field

The recent two-photon interference experiments by Wang, Zou, and Mandel, with and without a time-dependent light switch introduced into one of interferometer arms, indicate the collapse of photon waves along empty arms, not travelled by the detected photon, at a critical moment on the light cone backwards from the detected photon. It is proposed to interpret the Schrodinger's retarded wave equation as an operator acting on the advanced field satisfying the final condition of the experiment. In this time-symmetrical formulation the advanced field of the detected particle guides the retarded wave from the particle source not to enter empty arms, and the critical moment is interpreted as the time of the passage of the advanced field through the light switch. By changing the relative optical lengths of interferometer arms and observing the independence of the result of the experiment on the relative position of the detectors, we could conceive of the unarousal of the empty wave destined to collapse.

Reply to "Comment on 'Einstein-Podolsky-Rosen state for space-time variables in a two-photon interference experiment' "

The assertion of Kwait, Steinberg, and Chiao [preceding Comment, Phys. Rev. A 48, 3999 (1993)] that alignment problems and the size of the beam-defining irises explain the decrease in the visibility in two-photon interference experiments is examined. We argue that these effects can explain the reason that the visibility does not attain its maximum theoretical value, but that it fails to explain the decrease in the visibility with the path differences in the interferometers. We conclude that one explanation of this effect is the breakdown of perfect frequency phase matching in parametric down-conversion.

Comment on "Einstein-Podolsky-Rosen state for space-time variables in a two-photon interference experiment"

Comment on "Einstein-Podolsky-Rosen state for space-time variables in a two-photon interference experiment"

High-visibility interference in a Bell-inequality experiment for energy and time.

We report on a two-photon interference experiment proposed by Franson [Phys. Rev. Lett. 62, 2205 (1989)], in which sinusoidal fringes with visibilities greater than 70.7%, such as those predicted by quantum mechanics, violate a Bell inequality. We observe visibility of 80.4\ifmmode\pm\else\textpm\fi{}0.6%, implying a violation of the inequality by 16 standard deviations. Here the elements of reality under consideration are energy and time rather than spin components. Any classical field models describing separate beams in a Franson interferometer are limited to visibilities less than 50%, and hence ruled out as well, without the need for any supplementary assumptions.

Einstein-Podolsky-Rosen state for space-time variables in a two-photon interference experiment.

A pair of correlated photons generated from parametric down-conversion was sent to two independent Michelson interferometers. Second-order interference was studied by means of a coincidence measurement between the outputs of two interferometers. The reported experiment and analysis studied this second-order interference phenomenon from the point of view of the Einstein-Podolsky-Rosen (EPR) paradox. The experiment was done in two steps. The first step of the experiment used 50-psec and 3-nsec coincidence time windows simultaneously. The 50-psec window was able to distinguish a 1.5-cm optical path difference in the interferometers. The interference visibility was measured to be 38% and 21% for the 50-psec time window and 22% and 7% for the 3-nsec time window, when the optical path differences of the interferometers were 2 cm and 4 cm, respectively. By comparing the visibilities between these two windows, the experiment showed the nonclassical effect which resulted from an EPR state. The second step of the experiment used a 20-psec coincidence time window, which was able to distinguish a 6-mm optical path difference in the interferometers. The interference visibilities were measured to be 59% for an optical path difference of 7 mm. This is an observation of visibility greater than 50% for a two-interferometer EPR experiment which demonstrates nonclassical correlation of space-time variables.

Observation of a "quantum eraser": A revival of coherence in a two-photon interference experiment.

We have observed an effect known as a quantum eraser, using a setup similar to one previously employed to demonstrate a violation of Bell's inequalities. In this effect, an interfering system is first rendered incoherent by making the alternate Feynman paths which contribute to the overall process distinguishable; with our apparatus this is achieved by placing a half wave plate in one arm of a Hong-Ou-Mandel interferometer so as to rotate the polarization of the light in that arm by 90\ifmmode^\circ\else\textdegree\fi{}. This adds information to the system, in that polarization is a new parameter which serves to label the path of a given photon, even after a recombining beam splitter. The quantum ``eraser'' removes this information from the state vector, after the output port of the interferometer, but in time to cause interference effects to reappear upon coincidence detection. For this purpose, we use two polarizers in front of our detectors. We present experimental results showing how the degree of erasure (which determines the visibility of the interference) depends on the relative orientation of the polarizers, along with theoretical curves. In addition, we show how this procedure may do more than merely erase, in that the act of ``pasting together'' two previously distinguishable paths can introduce a new relative phase between them.

Models of a two-photon Einstein-Podolsky-Rosen interference experiment.

Models of a two-photon interference experiment proposed by Franson to study the Einstein-Podolsky-Rosen (EPR) effect are presented. The experiment considers a pair of photons correlated in time and in frequency, each of which is passed through an interferometer. When the path difference through the two interferometers is set so there is no first-order interference, Franson showed that second-order interference between the two photons could occur with 100% visibility. In this paper both quantum and classical models are considered and the importance of the coincidence time window and the effect of the frequency correlation are shown. Calculations are presented for all settings of the interferometers. The EPR effect arises from entangled states; a brief discussion is given of the nature of the entangled state for this type of experiment.

Experimental test of the de Broglie guided-wave theory for photons.

A two-photon interference experiment has been carried out, based on an idea recently proposed by Croca, Garuccio, Lepore, and Moreira. The experiment is designed to test a prediction of the de Broglie guided-wave theory, according to which the waves have a physical reality in addition to yielding photon detection probabilities. The results clearly contradict the de Broglie theory, but are consistent with conventional quantum mechanics.