700 research outputs found
Creation, storage, and on-demand release of optical quantum states with a negative Wigner function
Highly nonclassical quantum states of light, characterized by Wigner
functions with negative values, have been created so far only in a heralded
fashion. In this case, the desired output emerges rarely and randomly from a
quantum-state generator. An important example is the heralded production of
high-purity single-photon states, typically based on some nonlinear optical
interaction. In contrast, on-demand single-photon sources were also reported,
exploiting the quantized level structure of matter systems. These sources,
however, lead to highly impure output states, composed mostly of vacuum. While
such impure states may still exhibit certain single-photon-like features such
as anti-bunching, they are not enough nonclassical for advanced quantum
information processing. On the other hand, the intrinsic randomness of pure,
heralded states can be circumvented by first storing and then releasing them on
demand. Here we propose such a controlled release, and we experimentally
demonstrate it for heralded single photons. We employ two optical cavities,
where the photons are both created and stored inside one cavity, and finally
released through a dynamical tuning of the other cavity. We demonstrate storage
times of up to 300 ns, while keeping the single-photon purity around 50% after
storage. This is the first demonstration of a negative Wigner function at the
output of an on-demand photon source or a quantum memory. In principle, our
storage system is compatible with all kinds of nonclassical states, including
those known to be essential for many advanced quantum information protocols.Comment: 14 pages, 5 figure
Deterministic creation of entangled atom-light Schr\"odinger-cat states
Quantum physics allows for entanglement between microscopic and macroscopic
objects, described by discrete and continuous variables, respectively. As in
Schr\"odinger's famous cat gedanken experiment, a box enclosing the objects can
keep the entanglement alive. For applications in quantum information
processing, however, it is essential to access the objects and manipulate them
with suitable quantum tools. Here we reach this goal and deterministically
generate entangled light-matter states by reflecting a coherent light pulse
with up to four photons on average from an optical cavity containing one atom.
The quantum light propagates freely and reaches a remote receiver for quantum
state tomography. We produce a plethora of quantum states and observe
negative-valued Wigner functions, a characteristic sign of non-classicality. As
a first application, we demonstrate a quantum-logic gate between an atom and a
light pulse, with the photonic qubit encoded in the phase of the light field.Comment: includes Methods and Supplementary Informatio
Purification of photon subtraction from continuous squeezed light by filtering
Photon subtraction from squeezed states is a powerful scheme to create good
approximation of so-called Schr\"odinger cat states. However, conventional
continuous-wave-based methods actually involve some impurity in squeezing of
localized wavepackets, even in the ideal case of no optical losses. Here we
theoretically discuss this impurity, by introducing mode-match of squeezing.
Furthermore, here we propose a method to remove this impurity by filtering the
photon-subtraction field. Our method in principle enables creation of pure
photon-subtracted squeezed states, which was not possible with conventional
methods.Comment: 10 pages, 6 figure
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