25 research outputs found
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
Generation of optical Schr\"{o}dinger's cat states by generalized photon subtraction
We propose a high-rate generation method of optical Schr\"{o}dinger's cat
states. Thus far, photon subtraction from squeezed vacuum states has been a
standard method in cat-state generation, but its constraints on experimental
parameters limit the generation rate. In this paper, we consider the state
generation by photon number measurement in one mode of arbitrary two-mode
Gaussian states, which is a generalization of conventional photon subtraction,
and derive the conditions to generate high-fidelity and large-amplitude cat
states. Our method relaxes the constraints on experimental parameters, allowing
us to optimize them and attain a high generation rate. Supposing realistic
experimental conditions, the generation rate of cat states with large
amplitudes ( can exceed megacounts per second, about to
times better than typical rates of conventional photon subtraction. This
rate would be improved further by the progress of related technologies. Ability
to generate non-Gaussian states at a high rate is important in quantum
computing using optical continuous variables, where scalable computing
platforms have been demonstrated but preparation of non-Gaussian states of
light remains as a challenging task. Our proposal reduces the difficulty of the
state preparation and open a way for practical applications in quantum optics.Comment: 8 pages, 5 figure
Gaussian breeding for encoding a qubit in propagating light
Practical quantum computing requires robust encoding of logical qubits in
physical systems to protect fragile quantum information. Currently, the lack of
scalability limits the logical encoding in most physical systems, and thus the
high scalability of propagating light can be a game changer for realizing a
practical quantum computer. However, propagating light also has a drawback: the
difficulty of logical encoding due to weak nonlinearity. Here, we propose
Gaussian breeding that encodes arbitrary Gottesman-Kitaev-Preskill (GKP) qubits
in propagating light. The key idea is the efficient and iterable generation of
quantum superpositions by photon detectors, which is the most widely used
nonlinear element in quantum propagating light. This formulation makes it
possible to systematically create the desired qubits with minimal resources.
Our simulations show that GKP qubits above a fault-tolerant threshold,
including ``magic states'', can be generated with a high success probability
and with a high fidelity exceeding 0.99. This result fills an important missing
piece toward practical quantum computing.Comment: 19 pages, 2 figure
Single-shot single-mode optical two-parameter displacement estimation beyond classical limit
Uncertainty principle prohibits the precise measurement of both components of
displacement parameters in phase space. We have theoretically shown that this
limit can be beaten using single-photon states, in a single-shot and
single-mode setting [F. Hanamura et al., Phys. Rev. A 104, 062601 (2021)]. In
this paper, we validate this by experimentally beating the classical limit. In
optics, this is the first experiment to estimate both parameters of
displacement using non-Gaussian states. This result is related to many
important applications, such as quantum error correction.Comment: 5 pages, 4 figure