Efficient production of large-size optical Schr\xf6dinger cat states

Evgeny V Mikheev,Alexander S Pugin,Dmitry A Kuts,Sergey A Podoshvedov,Nguyen Ba An

doi:10.1038/s41598-019-50703-1

Evgeny V Mikheev, Alexander S Pugin + Show 3 more

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We present novel theory of effective realization of large-size optical Schrödinger cat states, which play an important role for quantum communication and quantum computation in the optical domain using laser sources. The treatment is based on the α-representation in infinite Hilbert space which is the decomposition of an arbitrary quantum state in terms of displaced number states characterized by the displacement amplitude α. We find analytical form of the α-representation for both even and odd Schrödinger cat states which is essential for their generation schemes. Two schemes are proposed for generating even/odd Schrödinger cat states of large size |β| (|β| ≥ 2) with high fidelity F (F ≈ 0.99). One scheme relies on an initially offline prepared two-mode entangled state with a fixed total photon number, while the other scheme uses separable photon Fock states as the input. In both schemes, generation of the desired states is heralded by the corresponding measurement outcomes. Conditions for obtaining states useful for quantum information processing are established and success probabilities for their generation are evaluated.

Highlights

It is known that a potentially quantum computer can effectively implement intractable algorithms such as large integer factoring1 and unsorted data search2 which cannot be effectively implemented by computers operating under classical laws
One can hardly say that the issue of optical quantum information processing (QIP) has been resolved7 and the question of how to efficiently exploit the optical resources for QIP remains of great interest
The DV-CV approach with the so-called hybrid states turns out to be a promising direction since the combination of two different physical systems could provide new capabilities to more efficiently implement optical quantum protocols27–36

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Introduction

It is known that a potentially quantum computer can effectively implement intractable algorithms such as large integer factoring1 and unsorted data search2 which cannot be effectively implemented by computers operating under classical laws. Photon subtraction from the displaced number state52,53 of the original entangled one in auxiliary mode allows one to generate the states that under certain conditions approximate either even or odd large-size SCSs with fidelity close to or even more of 0.99 that are suitable for quantum protocols.

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