32 research outputs found
Frequency tuning of a squeezed vacuum state using interferometric enhanced Bragg diffraction effect
We experimentally demonstrate the optical frequency tuning of a squeezed
vacuum state generated from an optical parametric oscillator by using an
acousto-optic modulator based bi-frequency interferometer. The systematic
efficiency of the frequency tuning device is , which is only confined by
the optical transmission efficiency of the acousto-optic modulators. The amount
of frequency tuning is 80 MHz, which is orders of magnitude larger than the
line-width of the laser used to generate the squeezed state, and can in
principle be further extended to GHz range. Our investigation shows the
interferometric enhanced Bragg diffraction effect can be applied to a variety
of other quantum optical states as well, and will serve as a handy tool for
quantum network.Comment: 8 pages, 5 figure
An acousto-optic modulator based bi-frequency interferometer for quantum technology
Acousto-optic modulators (AOMs) have been widely used in quantum optical
technology, but the non-ideal diffraction efficiency limits its application in
a quantum system. Here we demonstrate a bi-frequency interferometer using AOMs
as both the beam-splitter and the beam-combiner. The intensity of the input
light can be as low as the single photon level, and the interferometer can work
in a chopped phase locking mode. The modulation for the phase locking scheme is
realized on the beam-splitting AOM driven by specially designed radio frequency
signal, which avoids using extra optical modulators and makes the quantum
efficiency of the system as high as . By optimizing the factors
that affect the mode matching, the visibility of the beating signal for the
interferometer is . This near prefect visibility allows the
interferometer to be applied in high efficiency quantum technical schemes while
leaving the diffraction efficiencies of each AOM for about . This greatly
reduced the demand for the driving of AOMs.Comment: 6 pages, 4 figure
Complete temporal mode analysis in pulse-pumped ļ¬ber-optical parametric ampliļ¬er for continuous variable entanglement generation
Mode matching plays an important role in measuring the continuous variable entanglement. For the signal and idler twin beams generated by a pulse pumped fiber optical parametric amplifier (FOPA), the spatial mode matching is automatically achieved in single mode fiber, but the temporal mode property is complicated because it is highly sensitive to the dispersion and the gain of the FOPA. We study the temporal mode structure and derive the input-output relation for each temporal mode of signal and idler beams after decomposing the joint spectral function of twin beams with the singular-value decomposition method. We analyze the measurement of the quadrature-amplitude entanglement, and find mode matching between the multi-mode twin beams and the local oscillators of homodyne detection systems is crucial to achieve a high degree of entanglement. The results show that the noise contributed by the temporal modes nonorthogonal to local oscillator may be much larger than the vacuum noise, so the mode mis-match can not be accounted for by merely introducing an effective loss. Our study will be useful for developing a source of high quality continuous variable entanglement by using the FOPA
Multi-mode quantum correlation generated from an unbalanced SU(1,1) interferometer using ultra-short laser pulses as pump
Multi-mode entanglement is one of the critical resource in quantum
information technology. Generating large scale multi-mode entanglement state by
coherently combining time-delayed continuous variables Einstein-Podolsky-Rosen
pairs with linear beam-splitters has been widely studied recently. Here we
theoretically investigate the multi-mode quantum correlation property of the
optical fields generated from an unbalanced SU(1,1) interferometer pumped
ultra-short pulses, which generates multi-mode entangled state by using a
non-degenerate parametric processes to coherently combine delayed
Einstein-Podolsky-Rosen pairs in different frequency band. The covariance
matrix of the generated multi-mode state is derived analytically for arbitrary
mode number within adjacent timing slot, which shows a given mode is
maximally correlated to 5 other modes. Based on the derived covariance matrix,
both photon number correlation and quadrature amplitude correlation of the
generated state is analyzed. We also extend our analyzing method to the scheme
of generating entangled state by using linear beam splitter as a coherent
combiner of delayed EPR pairs, and compare the states generated by the two
coherently combining schemes. Our result provides a comprehensive theoretical
description on the quantum correlations generated from an unbalanced SU(1,1)
interferometer within Gaussian system range, and will offer more perspectives
to quantum information technology.Comment: 13 pages, 4 figure
Effect of chromatic dispersion induced chirp on the temporal coherence property of individual beam from spontaneous four wave mixing
Temporal coherence of individual signal or idler beam, determined by the
spectral correlation property of photon pairs, is important for realizing
quantum interference among independent sources. To understand the effect of
chirp on the temporal coherence property, two series of experiments are
investigated by introducing different amount of chirp into either the pulsed
pump or individual signal (idler) beam. In the first one, based on spontaneous
four wave mixing in a piece of optical fiber, the intensity correlation
function of the filtered individual signal beam, which characterizes the degree
of temporal coherence, is measured as a function of the chirp of pump. The
results demonstrate that the chirp of pump pulses decreases the degree of
temporal coherence. In the second one, a Hong-Ou-Mandel type two-photon
interference experiment with the signal beams generated in two different fibers
is carried out. The results illustrate that the chirp of individual beam does
not change the temporal coherence degree, but affect the temporal mode
matching. To achieve high visibility, apart from improving the coherence degree
by minimizing the chirp of pump, mode matching should be optimized by managing
the chirps of individual beams.Comment: 17pages, 4figure
Quantum information tapping using a fiber optical parametric amplifier with noise figure improved by correlated inputs
One of the important function in optical communication system is the
distribution of information encoded in an optical beam. It is not a problem to
accomplish this in a classical system since classical information can be copied
at will. However, challenges arise in quantum system because extra quantum
noise is often added when the information content of a quantum state is
distributed to various users. Here, we experimentally demonstrate a quantum
information tap by using a fiber optical parametric amplifier (FOPA) with
correlated inputs, whose noise is reduced by the destructive quantum
interference through quantum entanglement between the signal and the idler
input fields. By measuring the noise figure of the FOPA and comparing with a
regular FOPA, we observe an improvement of 0.7+-0.1 dB and 0.84+-0.09 dB from
the signal and idler outputs, respectively. When the low noise FOPA functions
as an information splitter, the device has a total information transfer
coefficient of Ts+Ti=1.47+-0.2, which is greater than the classical limit of 1.
Moreover, this fiber based device works at the 1550 nm telecom band, so it is
compatible with the current fiber-optical network.Comment: 28 pages, 6 figure
Quantum entangled Sagnac interferometer
SU(1,1) interferometer (SUI) is a novel type of interferometer that uses
directly entangled quantum fields for sensing phase change. For rotational
sensing, Sagnac geometry is usually adopted. However, because SUI depends on
the phase sum of the two arms, traditional Sagnac geometry, when applied to
SUI, will result in null signal. In this paper, we modify the traditional
Sagnac interferometer by nesting SU(1,1) interferometers inside. We show that
the rotational signal comes from two parts labeled as "classical" and
"quantum", respectively, and the quantum part, where quantum entangled fields
are used for sensing, has rotational signal enhanced by a factor related to the
gain of the SUI.Comment: 5 pages, 3 figure