We review quantum architectures for engineering the N00N state, a bipartite maximally entangled state essential in quantum metrology. These schemes transform the initial state |N⟩⊗|0⟩ into the N00N state, 12(|N⟩⊗|0⟩+|0⟩⊗|N⟩), where |N⟩ and |0⟩ are Fock states with N and 0 excitations, respectively. We demonstrate that this state can be generated through superpositions of quantum light modes, hybrid light–matter interactions, or spin ensembles. Our approach also enables the creation of mesoscopic and macroscopic entangled states, including entangled coherent and squeezed states. Furthermore, we show that a broad class of maximally entangled states can be realized within this framework. Extensions to multi-mode state engineering are also explored.
We review quantum architectures for engineering the N00N state, a bipartite maximally entangled state essential in quantum metrology. These schemes transform the initial state |N⟩⊗|0⟩ into the N00N state, 12(|N⟩⊗|0⟩+|0⟩⊗|N⟩), where |N⟩ and |0⟩ are Fock states with N and 0 excitations, respectively. We demonstrate that this state can be generated through superpositions of quantum light modes, hybrid light–matter interactions, or spin ensembles. Our approach also enables the creation of mesoscopic and macroscopic entangled states, including entangled coherent and squeezed states. Furthermore, we show that a broad class of maximally entangled states can be realized within this framework. Extensions to multi-mode state engineering are also explored.
Here, we review some quantum architectures designed for the engineering of the N00N state, a bipartite maximally entangled state crucial in quantum metrology applications. The fundamental concept underlying these schemes is the transformation of the initial state ∣N⟩⊗∣0⟩ to the N00N state 21(∣N⟩⊗∣0⟩+∣0⟩⊗∣N⟩), where ∣N⟩ and ∣0⟩ are the Fock states with N and 0 excitations. We show that this state can be generated as a superposition of modes of quantum light, a combination of light and motion, or a superposition of two spin ensembles. The approach discussed here can generate mesoscopic and macroscopic entangled states, such as entangled coherent and squeezed states, as well. We show that a large class of maximally entangled states can be achieved in such an architecture. The extension of these state engineering methods to the multi-mode setting is also discussed.
Quantum entanglement is central to many quantum technologies and is an indispensable ingredient of quantum information theory. These facts make the generation, characterization and quantification of entangled states unavoidable tasks, beside all their fundamental significance. As a particular example of such applications one may consider quantum metrology in which quantum entanglement is shown to have a significant role for beating the classical limits. However, generation, characterization and quantification of suitable entangled states are challenging tasks, in general.\n\nIn this dissertation, we introduce new platforms for engineering multipartite entangled states that are shown to be useful for quantum information processing and quantum metrology applications. In particular, we introduce new methods which can be used for generating N00N states, as one of the most challenging states to generate, enabling realization of such states in both photonic and spintronic architectures. We sketch a rather generic quantum circuit, for the N00N state generation, that could be realized in various quantum systems. Furthermore, we extend the platform for the generation of states beyond the N00N state. Typical examples of such sates could be entangled coherent or squeezed states, for instance, that of specific importance for quantum information and metrology applications. Furthermore, we extend the protocol for the multipartite state scenario. Also, we demonstrate that attaining the ultimate sensitivity in phase estimation is not an exclusive property of the N00N states. As a result, we find a large class of entangled states that could provide us with the ultimate sensitivity achieved by the N00N state.\n\nAs a part of our effort for the N00N state generation, we develop a new scheme where N00N states could be realized in two ensembles of nitrogen--vacancy (NV) centers in diamond. This could be interesting by noting the fact that NV centers in diamonds provide a remarkably long coherence time, even at the room temperature. This opens up new possibilities for protecting N00N states against decoherence.\n\nMoreover, having the long coherence time of the ensembles of the NV centers, we show that a hybrid quantum system consisting of three ensembles of NV centers coupled to a superconducting device enables the generation of controllable macroscopic multipartite entangled states, which could be used as a building block for quantum networks.\n\nFurthermore, we investigate entanglement of nonorthogonal states in details, and more specifically, we obtain a closed-form analytical expression for the entanglement degree of a multipartite qutrit state, that offers a quantitative measure for entanglement n-mode nonorthogonal qutrit states with an arbitrary n. Such higher dimensional entangled states could be useful in quantum communication protocols.\n\n Finally, we introduce a new configuration where any pair of quantum states can perfectly be swapped between two quantum resonators enabling a realization of a universal swap operation in photonics systems. This can serve as a building block of various quantum information processors.
Quantum states of light, such as squeezed states or entangled states, can be used to make measurements (metrology), produce images, and sense objects with a precision that far exceeds what is possible classically, and also exceeds what was once thought to be possible quantum mechanically. The primary idea is to exploit quantum effects to beat the shot-noise limit in metrology and the Rayleigh diffraction limit in imaging and sensing. Quantum optical metrology has received a boost in recent years with an influx of ideas from the rapidly evolving field of optical quantum information processing. Both areas of research exploit the creation and manipulation of quantum-entangled states of light. We will review some of the recent theoretical and experimental advances in this exciting new field of quantum optical metrology, focusing on examples that exploit a particular two-mode entangled photon state – the High-N00N state.
An ensemble of nitrogen-vacancy (NV) centers coupled to a circuit QED device is shown to enable an efficient, high-fidelity generation of high-N00N states. Instead of first creating entanglement and then increasing the number of entangled particles N, our source of high-N00N states first prepares a high-N Fock state in one of the NV ensembles and then entangles it to the rest of the system. With such a strategy, high-N N00N states can be generated in just a few operational steps with an extraordinary fidelity. Once prepared, such a state can be stored over a longer period of time due to the remarkably long coherence time of NV centers.
We show how an idealized measurement procedure can condense photons from two modes into one and how, by feeding forward the results of the measurement, it is possible to generate efficiently superposition states commonly called N00N states. For the basic procedure sources of number states leak onto a beam splitter, and the output ports are monitored by photodetectors. We find that detecting a fixed fraction of the input at one output port suffices to direct the remainder to the same port, with high probability, however large the initial state. When instead photons are detected at both ports, macroscopic quantum superposition states are produced. We describe a linear-optical circuit for making the components of such a state orthogonal, and another to convert the output to a N00N state. Our approach scales exponentially better than existing proposals. Important applications include quantum imaging and metrology.
Multi-photon entangled states of light such as N00N (N is the photon number) and squeezed states are routinely used in quantum metrological experiments. Spatially structuring these quantum optical states improves the sensitivity and enhances resolution by using the high dimensional spatial degree of freedom. However, progress in quantum structured light mainly focused on either increasing the number of photons, or increasing the mode numbers, separately [1]. The reason is that generating high (mode number>> 10) dimensional structured light states is usually a lossy process that degrades multi-photon states of light.