We propose a new method, "counter-factual" carving, that uses the "no-jump" evolution of a probe to generate entangled many-body states of high fidelity. The probe is coupled to a target ensemble of qubits and engineered to exponentially decay at a rate depending on the target collective spin, such that post-selecting on observing no probe decay precisely removes select faster-decaying spin components. When probe and
N-qubit target interact via a cavity mode of cooperativity
C, counter-factual carving generates entangled states with infidelities of
e−C/N, an exponential improvement over previous carving schemes. Counter-factual carving can generate complex entangled states for applications in quantum metrology and quantum computing.
We propose a method that uses the ``no-jump'' evolution of a probe to generate entangled multiparticle states of high fidelity. The probe is coupled to a target ensemble of qubits and engineered to exponentially decay at a rate depending on the target collective spin, such that postselecting on observing no probe decay precisely removes select faster-decaying spin components. When a probe and
N-qubit target interact via a cavity mode of cooperativity
C, our procedure generates entangled states with infidelities of ${e}^{\ensuremath{-}C/N}$, an exponential improvement over previous carving schemes. This scheme, which we call ``counterfactual'' carving, can generate complex entangled states for applications in quantum metrology and quantum computing.