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Register a new userTunable quantum interference: How to make morning, noon, and afternoon states
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We show that the N-photon states produced by interference between laser light and downconverted light at the input of a two path interferometer can be characterized by a single tuning parameter that describes a transition from phase squeezing to nearly maximal path entanglement and back. The quantum states are visualized on a sphere using the analogy between N-photon interference and the spin-N/2 algebra.
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This is a story about making quantum computers speak, and doing so in a quantum-native, compositional and meaning-aware manner. Recently we did question-answering with an actual quantum computer. We explain what we did, stress that this was all done in terms of pictures, and provide many pointers to the related literature. In fact, besides natural language, many other things can be implemented in a quantum-native, compositional and meaning-aware manner, and we provide the reader with some indications of that broader pictorial landscape, including our account on the notion of compositionality. We also provide some guidance for the actual execution, so that the reader can give it a go as well.
NOON state interference (NOON-SI) is a powerful tool to improve the phase sensing precision, and plays an important role in quantum measurement. In most of the previous NOON-SI experiments, the measurements were performed in time domain where the spectral information of the involved photons was integrated and lost during the measurement. In this work, we experimentally measured the joint spectral intensities (JSIs) at different positions of the interference patterns in both time and frequency domains. It was observed that the JSIs were phase-dependent and show odd (even)-number patterns at $0$ ($pi$) phase shift; while no interference appeared in time domain measurement, the interference pattern clearly appeared in frequency domain. To our best knowledge, the latter is the first observation of the spectrally resolved NOON state interference, which provides alternative information that cannot be extracted from the time-domain measurement. To explore its potential applications, we considered the interferometric sensing with our setup. From the Fisher information-based analysis, we show that the spectrally resolved NOON-SI has a better performance at non-zero-delay position than its non-spectrally resolved counterpart. The spectrally resolved NOON-SI scheme may be useful for quantum metrology applications such as quantum phase sensing, quantum spectroscopy, and remote synchronization.
NOON states are path entangled states which can be exploited to enhance phase resolution in interferometric measurements. In the present paper we analyze the quantum states obtained by optical parametric amplification of polarization NOON states. First we study, theoretically and experimentally, the amplification of a 2-photon state by a collinear Quantum Injected Optical Parametric Amplifier (QIOPA). We compared the stimulated emission regime with the spontaneous one, studied by Sciarrino et al. (PRA 77, 012324), finding comparable visibilities between the two cases but an enhancement of the signal in the stimulated case. As a second step, we show that the collinear amplifier cannot be successfully used for amplifying N-photon states with N>2 due to the intrinsic lambda/4 oscillation pattern of the crystal. To overcome this limitation, we propose to adopt a scheme for the amplification of a generic state based on a non-collinear QIOPA and we show that the state obtained by the amplification process preserves lambda/N feature and exhibits a high resilience to losses. Furthermore, an asymptotic unity visibility can be obtained when correlation functions with sufficiently high order M are analyzed.
We introduce the `displacemon electromechanical architecture that comprises a vibrating nanobeam, e.g. a carbon nanotube, flux coupled to a superconducting qubit. This platform can achieve strong and even ultrastrong coupling enabling a variety of quantum protocols. We use this system to describe a protocol for generating and measuring quantum interference between two trajectories of a nanomechanical resonator. The scheme uses a sequence of qubit manipulations and measurements to cool the resonator, apply an effective diffraction grating, and measure the resulting interference pattern. We simulate the protocol for a realistic system consisting of a vibrating carbon nanotube acting as a junction in a superconducting qubit, and we demonstrate the feasibility of generating a spatially distinct quantum superposition state of motion containing more than $10^6$ nucleons.
Structured photons are nowadays an interesting resource in classical and quantum optics due to the richness of properties they show under propagation, focusing and in their interaction with matter. Vectorial modes of light in particular, a class of modes where the polarization varies across the beam profile, have already been used in several areas ranging from microscopy to quantum information. One of the key ingredients needed to exploit the full potential of complex light in quantum domain is the control of quantum interference, a crucial resource in fields like quantum communication, sensing and metrology. Here we report a tunable photon-photon interference between vectorial modes of light. We demonstrate how a properly designed spin-orbit device can be used to control quantum interference between vectorial modes of light by simply adjusting the device parameters and no need of interferometric setups. We believe our result can find applications in fundamental research and quantum technologies based on structured light by providing a new tool to control quantum interference in a compact, efficient and robust way.
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