Tunable non-Gaussian resources for continuous-variable quantum technologies

Abstract

We introduce and discuss a set of tunable two-mode states of continuous-variable systems, as well as a simple, effective scheme for their experimental generation. This class of tunable entangled resources is defined by a general ansatz depending on two experimentally adjustable parameters. It is very ample and flexible as it encompasses Gaussian as well as non-Gaussian states. The latter include, among others, known states such as squeezed number states and de-Gaussified photon-added and photon-subtracted squeezed states, the latter being the most efficient non-Gaussian resources currently available in the laboratory. Moreover, it contains the classes of squeezed Bell states and even more general non-Gaussian resources that can be optimized according to the specific quantum technological task that needs to be realized. The proposed experimental scheme exploits linear optical operations and photon detections performed on a pair of uncorrelated two-mode Gaussian squeezed states. The desired non-Gaussian state is then realized via ancillary squeezing and conditioning. Two independent, freely tunable experimental parameters can be exploited to generate different states and to optimize the performance in implementing a given quantum protocol. As a concrete instance, we analyze in detail the performance of different states considered as resources for the realization of quantum teleportation in realistic conditions. For the fidelity of teleportation of an unknown coherent state, we show that the resources associated with the optimized parameters outperform, in a significant range of experimental values, both Gaussian twin beams and photon-subtracted squeezed states.

Reliable quantum certification of photonic state preparations

“…Furthermore, a variety of non-Gaussian states paradigmatic in quantum optics and quantum information are also covered by our protocol (see Section S2 in the SI for details). These include, for instance, de-Gaussified photon-subtracted multi-mode Gaussian states [34][35][36][37] , multi-mode squeezed Gaussian states postselected through photon-number or quadrature measurements, as in finite-squeezing cluster-state qumode quantum computers 40,41 , and linear-optical network outputs post-selected though photon-number measurements, ranging from photon -added or -subtracted linear-optical network states to all the states preparable with Knill-Laflamme-Milburn-like schemes 38,39 . For all such states, our test is efficient in the inverse post-selection success probability 1/P(φ A | t ).…”

“…This class includes crucial non-Gaussian resources for quantum information and quantum optics. For instance, when the post-selection is in the Fock basis, it encompasses de-Gaussified photon-subtracted squeezed Gaussian states [34][35][36][37] . Furthermore, if apart from Fock-basis measurements, the post-selection uses also quadrature homodyne measurements, C LPSG contains all the states accessible to finite-squeezing cluster-state qumode quantum computers 40,41 .…”

Teleportation-based noiseless quantum amplification of coherent states of light

“…This state can be prepared from a two-mode squeezed vacuum state by a modified joint photon subtraction from each mode, where an auxiliary weak two-mode squeezed vacuum state is injected into the auxiliary input ports of the beam splitters that serve for photon subtraction [38].…”

“…Fig.3. Preparation of entangled state for teleportation-based noiseless amplification via generalized photon subtraction[38]. The optical parametric amplifiers OPA generate two-mode squeezed vacuum states with different squeezing strengths 𝜆 and 𝜇.…”

Non-Gaussian entanglement swapping

“…For instance, optimized SB resources allow for a teleportation fidelity higher than that associated with resources such as Gaussian twin beams or non-Gaussian photon-subtracted squeezed states (these last being currently the best experimentally generated resources) for a large variety of teleported input states, including coherent, squeezed, and number states [12][13][14]. Simple schemes for the generation of SB states have been recently proposed, based on the exploitation of independent twin beams and suitable conditional coincidence measurements [65].…”