scholarly journals Engineering Schrödinger cat states with a photonic even-parity detector

Quantum ◽  
2020 ◽  
Vol 4 ◽  
pp. 239 ◽  
Author(s):  
G. S. Thekkadath ◽  
B. A. Bell ◽  
I. A. Walmsley ◽  
A. I. Lvovsky
Keyword(s):  
Time Reversal ◽  
Coherent States ◽  
Beam Splitter ◽  
Photon Number ◽  
Input State ◽  
Interference Phenomenon ◽  
Arbitrary Size ◽  
Two Component ◽  
Schrödinger Cat ◽  
Cat States

When two equal photon-number states are combined on a balanced beam splitter, both output ports of the beam splitter contain only even numbers of photons. Consider the time-reversal of this interference phenomenon: the probability that a pair of photon-number-resolving detectors at the output ports of a beam splitter both detect the same number of photons depends on the overlap between the input state of the beam splitter and a state containing only even photon numbers. Here, we propose using this even-parity detection to engineer quantum states containing only even photon-number terms. As an example, we demonstrate the ability to prepare superpositions of two coherent states with opposite amplitudes, i.e. two-component Schrödinger cat states. Our scheme can prepare cat states of arbitrary size with nearly perfect fidelity. Moreover, we investigate engineering more complex even-parity states such as four-component cat states by iteratively applying our even-parity detector.

Homodyne-like detection scheme based on photon-number-resolving detectors

2017 ◽  
Vol 15 (08) ◽  
pp. 1740016 ◽  
Author(s):  
Alessia Allevi ◽  
Matteo Bina ◽  
Stefano Olivares ◽  
Maria Bondani
Keyword(s):  
Coherent States ◽  
Beam Splitter ◽  
Photon Number ◽  
Local Oscillator ◽  
Quantum States ◽  
Homodyne Detection ◽  
Detection Scheme ◽  
Light Signals ◽  
The Difference ◽  
Signal Field

Homodyne detection is the most effective detection scheme employed in quantum optics to characterize quantum states. It is based on mixing at a beam splitter the signal to be measured with a coherent state, called the “local oscillator,” and on evaluating the difference of the photocurrents of two photodiodes measuring the outputs of the beam splitter. If the local oscillator is much more intense than the field to be measured, the homodyne signal is proportional to the signal-field quadratures. If the local oscillator is less intense, the photodiodes can be replaced with photon-number-resolving detectors, which have a smaller dynamics but can measure the light statistics. The resulting new homodyne-like detector acquires a hybrid nature, being it capable of yielding information on both the particle-like (statistics) and wave-like (phase) properties of light signals. The scheme has been tested in the measurement of the quadratures of coherent states, bracket states and phase-averaged coherent states at different intensities of the local oscillator.

scholarly journals Bracket states for communication protocols with coherent states

2014 ◽  
Vol 12 (02) ◽  
pp. 1461018 ◽  
Author(s):  
Alessia Allevi ◽  
Stefano Olivares ◽  
Maria Bondani
Keyword(s):  
Coherent States ◽  
Direct Detection ◽  
Photon Number ◽  
Fano Factor ◽  
Local Oscillator ◽  
Input State ◽  
Optical Elements ◽  
Symmetry Properties ◽  
Communication Scheme ◽  
Phase Sensitive

We present the generation and characterization of the class of bracket states, namely phase-sensitive mixtures of coherent states exhibiting symmetry properties in the phase-space description. A bracket state can be seen as the statistical ensemble arriving at a receiver in a typical coherent-state-based communication channel. We show that when a bracket state is mixed at a beam splitter with a local oscillator, both the emerging beams exhibit a Fano factor larger than 1 and dependent on the relative phase between the input state and the local oscillator. We discuss the possibility to exploit this dependence to monitor the phase difference for the enhancement of the performances of a simple communication scheme based on direct detection. Our experimental setup involves linear optical elements and a pair of photon-number-resolving detectors operated in the mesoscopic photon-number domain.

The generalized pair coherent states and the corresponding entangled coherent states

2015 ◽  
Vol 13 (08) ◽  
pp. 1550065
Author(s):  
Won Sang Chung
Keyword(s):  
Coherent States ◽  
Density Operator ◽  
Schwarz Inequality ◽  
Bell States ◽  
Photon Statistics ◽  
Schrödinger Cat ◽  
Cat States ◽  
Reduced Density ◽  
Entangled Coherent States

In this paper, we consider the generalized Schrödinger cat states. Using these states, we obtain the corresponding quasi-Bell states and the reduced density operator. For these quasi-Bell states, we investigate the non-classical effects such as oscillatory photon statistics, sub-Poissonian property and violation of the Cauchy–Schwarz inequality.

scholarly journals A TREATMENT OF THE QUANTUM PARTIAL ENTROPIES IN THE ATOM-FIELD INTERACTION WITH A CLASS OF SCHRÖDINGER CAT STATES

2005 ◽  
Vol 03 (03) ◽  
pp. 591-602 ◽  
Author(s):  
A.-S. F. OBADA ◽  
H. A. HESSIAN ◽  
MAHMOUD ABDEL-ATY
Keyword(s):  
Coherent State ◽  
Coherent States ◽  
Stark Shift ◽  
Initial State ◽  
Field Interaction ◽  
Composite State ◽  
Quantum Dynamical ◽  
Initial States ◽  
Schrödinger Cat ◽  
Cat States

This paper is an enquiry into the circumstances under which entropy and subentropy methods can give an answer to the question of quantum entanglement in the composite state. Using a general quantum dynamical system, we obtain the analytical solution when the atom initially starts from its excited state and the field in different initial states. Different features of the entanglement are investigated when the field is initially assumed to be in a coherent state, an even coherent state (Schrödinger cate state), and a statistical mixture of coherent states. Our results show that the setting of the initial state and the Stark shift play important roles in the evolution of the sub-entropies and entanglement.

scholarly journals Schrödinger cat states in circuit QED

2019 ◽  
pp. 402-427
Author(s):  
Steven M. Girvin
Keyword(s):  
Quantum Optics ◽  
Error Correction ◽  
Cavity Qed ◽  
Photon Number ◽  
Quantum Error Correction ◽  
Circuit Qed ◽  
Schrödinger Cat ◽  
Microwave Regime ◽  
Cat States ◽  
Quantum Error

Circuit quantum electrodynamics (‘circuit QED’) describes the quantum mechanics and quantum optics of superconducting electrical circuits operating in the microwave regime near absolute zero temperature. It is the analog of cavity QED in quantum optics with the role of the atoms being played by superconducting qubits. The present lecture notes present a brief overview of circuit QED and then focus on some of the novel quantum states that can be produced and measured (via photon number parity and the Wigner function) using the strong coupling between an artificial atom and one or more cavities. Of particular importance are Schrödinger cat states of photons. Despite long being considered exemplars of frail quantum superpositions that quickly decohere, such states have recently been used as the basis for quantum error correction codes which have reached the long-sought goal of enhancing the lifetime of quantum information through active quantum error correction.

q-Deformed Barut–Girardello su(1, 1) coherent states and Schrödinger cat states

2017 ◽  
Vol 193 (3) ◽  
pp. 1844-1852 ◽  
Author(s):  
Yuefeng Zhao ◽  
Yan Zeng ◽  
Honggang Liu ◽  
Qi Song ◽  
Gangcheng Wang ◽  
...  
Keyword(s):  
Coherent States ◽  
Schrödinger Cat ◽  
Cat States

scholarly journals Efficient production of large-size optical Schrödinger cat states

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Evgeny V. Mikheev ◽  
Alexander S. Pugin ◽  
Dmitry A. Kuts ◽  
Sergey A. Podoshvedov ◽  
Nguyen Ba An
Keyword(s):  
Quantum Information Processing ◽  
Photon Number ◽  
Analytical Form ◽  
Entangled State ◽  
Efficient Production ◽  
Large Size ◽  
Novel Theory ◽  
Laser Sources ◽  
Schrödinger Cat ◽  
Cat States

Abstract We present novel theory of effective realization of large-size optical Schrödinger cat states, which play an important role for quantum communication and quantum computation in the optical domain using laser sources. The treatment is based on the α-representation in infinite Hilbert space which is the decomposition of an arbitrary quantum state in terms of displaced number states characterized by the displacement amplitude α. We find analytical form of the α-representation for both even and odd Schrödinger cat states which is essential for their generation schemes. Two schemes are proposed for generating even/odd Schrödinger cat states of large size |β| (|β| ≥ 2) with high fidelity F (F ≈ 0.99). One scheme relies on an initially offline prepared two-mode entangled state with a fixed total photon number, while the other scheme uses separable photon Fock states as the input. In both schemes, generation of the desired states is heralded by the corresponding measurement outcomes. Conditions for obtaining states useful for quantum information processing are established and success probabilities for their generation are evaluated.

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