Demonstration of Quantum Telecloning of Optical Coherent States

We demonstrate unconditional telecloning for the first time. In particular, we symmetrically and unconditionally teleclone coherent states of light from one sender to two receivers, achieving a fidelity for each clone of $F=0.58\pm 0.01$, which surpasses the classical limit. This is a manipulation of a new type of multipartite entanglement whose nature is neither purely bipartite nor purely tripartite.

Figure 1

The experimental setup for quantum telecloning from Alice to Bob and Claire to produce clone 1 and 2. Modes i and ii are squeezed vacua and mode iii is a vacuum. The $g$’s are normalized information gains of classical channels. AM denotes an amplitude modulator and PM denotes a phase modulator. A 99%-reflectance beam splitter (denoted 1-99 BS) enables displacement transformations in phase space [5].

Figure 2

(a) Pump power dependence of squeezing and antisqueezing of the output of ${\mathrm{OPO}}_{\mathrm{i}}$. The squeezing and antisqueezing are measured at 1 MHz. Visibility at a 50-50 beam splitter for homodyne measurement is about 0.95 and quantum efficiency of the detector is more than 99%. (b) Calculated fidelities from the squeezing and antisqueezing.

Figure 3

Quantum telecloning from Alice to Bob and Claire. All traces are normalized to the corresponding vacuum noise levels. (a) Alice’s measurement results for $p$ quadrature. Trace i, the corresponding vacuum noise level $⟨(\Delta {\widehat{p}}^{(0)}{)}^2⟩=\frac{1}{4}$. Trace ii, the measurement result of a vacuum input $⟨({\widehat{p}}_v^{\prime }{)}^2⟩$, where ${\widehat{p}}_v^{\prime }=({\widehat{p}}_{\mathrm{in}}^{(0)}+{\widehat{p}}_{\mathrm{A}})/\sqrt{2}$. Trace iii, the measurement result of a coherent-state input $⟨({\widehat{p}}_v{)}^2⟩$ with the phase scanned. (b), (c) The measurement results of the telecloned states at Bob (b) and Claire (c) for $p$ quadratures ($x$ quadratures are not shown). Trace i, the corresponding vacuum noise levels. Trace ii, the telecloned states for a vacuum input $⟨(\Delta {\widehat{p}}_{1,2}{)}^2⟩$. Trace iii, the telecloned states for a coherent-state input. The measurement frequency is centered at 1 MHz, and the resolution and video bandwidths are 30 kHz and 300 Hz, respectively. All traces except for trace iii are averaged 20 times.