Tailor-made quantum states

Yasunobu Nakamura

Daniele Binosi, Giovanni Garberoglio, Diego Maragnano +2 more

Quantum state tomography (QST) aims at reconstructing the state of a quantum system. However, in conventional QST, the number of measurements scales exponentially with the number of qubits. Here, we propose a QST protocol, in which the introduction of a threshold allows one to drastically reduce the number of measurements required for the reconstruction of the state density matrix without compromising the result accuracy. In addition, one can also use the same approach to reconstruct an approximated density matrix tailoring the number of measurements on the available resources. We experimentally demonstrate this protocol by performing the tomography of states up to 7 qubits. We show that our approach can lead to results in agreement with those obtained by QST even when the number of measurements is reduced by more than two orders of magnitude.

Anonymous

Chiaki Ohae, Junpeng Zheng, Masaru Suzuki +2 more

We theoretically and experimentally show the tailor-made Raman-resonant four-wave-mixing process. We also demonstrate an attractive application of this tailored nonlinear frequency mixing as an optical device, namely, nonlinear Mach-Zehnder interferometer in the frequency domain.

Konrad Banaszek, Rafał Demkowicz-Dobrzański, Ian A. Walmsley

Stefan Gerlich, Sandra Eibenberger, Mathias Tomandl +6 more

The wave nature of matter is a key ingredient of quantum physics and yet it defies our classical intuition. First proposed by Louis de Broglie a century ago, it has since been confirmed with a variety of particles from electrons up to molecules. Here we demonstrate new high-contrast quantum experiments with large and massive tailor-made organic molecules in a near-field interferometer. Our experiments prove the quantum wave nature and delocalization of compounds composed of up to 430 atoms, with a maximal size of up to 60 Å, masses up to m=6,910 AMU and de Broglie wavelengths down to λdB=h/mv≃1 pm. We show that even complex systems, with more than 1,000 internal degrees of freedom, can be prepared in quantum states that are sufficiently well isolated from their environment to avoid decoherence and to show almost perfect coherence. Observing superposition states of mesoscopic quantum systems is an ongoing challenge. Gerlichet al. report quantum interference of large tailor-made organic compounds, demonstrating delocalization and the quantum wave nature of entire molecules composed of up to 430 atoms.