We present an experiment where a range of highly non‐classical optical states were generated and fully characterized. As a class they can be considered as realizations of a qubit state in a squeezed vacuum/squeezed photon basis. The central technique of displaced photon subtraction will have applications to quantum computing with coherent states.
We present an experiment where a range of highly non‐classical optical states were generated and fully characterized. As a class they can be considered as realizations of a qubit state in a squeezed vacuum/squeezed photon basis. The central technique of displaced photon subtraction will have applications to quantum computing with coherent states.
We investigate the practical scheme of engineering a qubit of two optical continuous-variable states, based on squeezed vacuum and coherently displaced photon subtraction. A fully multimode model is developed to describe a continuous wave (cw) setting of the experiment, which has been successfully implemented to generate highly pure non-classical states. The model agrees well with the experimental results and the numerical results show that the intrinsic imperfection due to the cw nature of the source is relatively small. Our photon subtraction technique could also be useful for preparing optical Schrödinger's cat-like states in arbitrary superposition, which is a basic qubit resource for linear optics coherent state quantum computing.
In a new branch of quantum computing, information is encoded into coherent states, the primary carriers of optical communication. To exploit it, quantum bits of these coherent states are needed, but it is notoriously hard to make superpositions of such continuous-variable states. We have realized the complete engineering and characterization of a qubit of two optical continuous-variable states. Using squeezed vacuum as a resource and a special photon-subtraction technique, we could with high precision prepare an arbitrary superposition of squeezed vacuum and a squeezed single photon. This could lead the way to demonstrations of coherent state quantum computing.
Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear χ2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong χ3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.
Engineering non-classical states of the electromagnetic field is a central quest for quantum optics(1,2). Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems(3). We focus here on the use of a continuous-wave optical parametric oscillator(3,4). This system is based on a non-linear χ(2) crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states(5). Generating directly such states is a difficult task and would require strong χ(3) non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.
Photonics quantum networks are pivotal for quantum technologies, facilitating efficient information distribution and manipulation through quantum states of light. Continuous-variable (CV) cluster states, essential resources for Measurement-Based Quantum Computing, can be deterministically generated using squeezed states of light and mode-basis changes [1]. However, Gaussian states like squeezed states or cluster states, can be efficiently simulated with a classical computer [2]. Thus, to achieve quantum advantage, non-Gaussianity should be introduced, which can be accomplished by subtracting a photon from a squeezed state [3].
Based on the coherent state (S1) and the operator [Formula: see text], we induce other three quantum states (here we abbreviate them as S2, S3 and S4). S2 is obtained by operating the operator on S1 directly. S3 is an orthogonal state of S1 constructed from the orthogonalizer relevant with that operator. S4 is a continuous-variable (CV) qubit state superposed from S1 and S3. We study and compare the mathematical and physical properties of such four quantum states. We demonstrate some statistical properties for S1–S4, including the mean photon number (MPN), anti-bunching effect, quadrate squeezing, photon number distribution, Husimi Q-function and Wigner function. The numerical results show some interesting non-classical characters for such states. It is worthy to note that the photon-added coherent state introduced by Agarwal and Tara is only a special case of our considered states.