Figure 1

(Color online) $N$-party single qubit secret sharing. A qubit (in our case a photon) is prepared in an initial state by the part $R_1$, using a single qubit source, and is sent sequentially, from $R_1$ to $R_N$, over the quantum channel, until it is measured by the last part $R_N$. Each party modulates the photon with a randomly chosen phase ${\varphi }_i(i=1,\dots ,N-1)$ between 0, $\pi ∕2$, $\pi$, or $3\pi ∕2$. The part $R_N$ measures with phase modulation choice ${\varphi }_N$ between 0 and $\pi ∕2$. In half of the cases the phases add up in such a way that the measurement results are deterministic, indicating a constructive or destructive interference. These cases can be used for the secret sharing.Reuse & Permissions

Figure 2

(Color online) Experimental setup for five-party phase encoded quantum secret sharing. For details, see the text. The setup does not show the control electronics layer and wavelength-division multiplexing (WDM) layer used to send synchronization and trigger from Alice to remaining parties. For this purpose a second pulsed laser with $1538\mathrm{nm}$ wavelength was used.Reuse & Permissions

Figure 3

(Color online) Polarization insensitive phase modulator. The $R$ output of the PBS denotes the reflected component (vertical), while the $T$ output denotes the transmitted component (horizontal).Reuse & Permissions

Figure 4

(Color online) Multiparty quantum secret sharing experimental results. (a) Quantum bit error rate $\left(Q_{\mathrm{BER}}\right)$ for three-party and four-party, (b) raw rate, both as a function of fiber length with $0.25\mathrm{dB}{\mathrm{km}}^{-1}$ loss and channel loss for three and four-party quantum secret sharing. The squares show measurement results for $\mu =0.1$, the triangles for $\mu =0.2$ and the dots for $\mu =0.3$. The theoretical curves were drawn for the following measured attenuation of the setup’s parts: $5\mathrm{dB}$ for Alice, Charlie, and David stations; $4.2\mathrm{dB}$ for the Elisabeth station. In both four-party and three-party setups the Bob station was not used. The total attenuation in the interconnecting FC contacts was measured to $1.8\mathrm{dB}$. The achieved visibilities were greater than 98.5%. All the measurements were carried out at the laser driver repetition rate $f_{\text{laser}}=2\mathrm{MHz}$. The efficient laser pulse frequency $f_{\mathrm{eff}}=d_{\text{cycle}}\times f_{\text{laser}}$ was lower due to the duty cycle $d_{\text{cycle}}=l_{\text{burst}}∕(l_{\text{burst}}+l_{\text{pause}})⩽0.5$, see Sec. 3.Reuse & Permissions