Universal Continuous-Variable State Orthogonalizer and Qubit Generator

Abstract

The superposition principle is at the heart of quantum mechanics and at the root of many paradoxes arising when trying to extend its predictions to our everyday world. Schrödinger's cat [1] is the prototype of such paradoxes and here, in contrast to many others, we choose to investigate it from the operational point of view. We experimentally demonstrate a universal strategy for producing an unambiguously distinguishable type of superposition, that of an arbitrary pure state and its orthogonal. It relies on only a limited amount of information about the input state to first generate its orthogonal one. Then, a simple change in the experimental parameters is used to produce arbitrary superpositions of the mutually orthogonal states. Constituting a sort of Schrödinger's black box, able to turn a whole zoo of input states into coherent superpositions, our scheme can produce arbitrary continuous-variable optical qubits, which may prove practical for implementing quantum technologies and measurement tasks.

Qubit-Programmable Operations on Quantum Light Fields

“…Differently from conditional gates, such as the controlled-NOT gate for two-qubits, we do not require that the programme state is preserved. Analogic control has been implemented using an optical displacement to modulate the probability amplitude of single-photon subtraction 11 13 31 , and extensions to optomechanics have been discussed 32 ; here we analyse a scheme for implementing the interface between a quantum optical field and the simplest discrete programme, a qubit 33 .…”

Conditional Hybrid Nonclassicality

“…In the following, we determine the coefficients (l) j for the weighted sampling formula (22) from the cumulative distribution P in Eq. (23). We need to satisfy the following two requirements: (i) The quadrature density p(x; ϕ (l) ) for a given phase is approximated by the relative frequencies of measurement outcomes x (l) j for this phase ϕ (l) ; (ii) The recovered quadrature distribution of phases is uniformly distributed.…”

“…Traditionally, the CV and DV representation of light have been individually exploited, but the connection between these two complementary regimes has not been extensively studied. One of the few relations between CV and DV systems that has been established is based on the observation that qubits can be constructed out of CV states [22,23]. Another early attempt to consider a hybrid system was elaborated to measure nonclassicality between a vibrational mode and the electronic states of a trapped two-level atom based on a Wigner matrix [24].…”

Coherent Superpositions of Photon Creation Operations and Their Application to Multimode States of Light

“…After its first experimental realization, photon addition has become an extraordinary new tool for manipulating light at the deepest level and, together with photon subtraction [5][6][7][8], it has allowed reaching an impressive degree of control in the engineering of the quantum state of light. Besides having been used for the verification of fundamental quantum rules [9][10][11], photon addition and subtraction, together with sequences and superpositions of these two operations, have allowed researchers to implement many new purely-quantum protocols, such as noiseless amplification [12], state orthogonalization and arbitrary continuousvariable (CV) qubit generation [13], emulation of Kerr nonlinearities at the single-photon level [14], etc.…”