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Author(s): Ji-Gang Ren [1, 2]; Ping Xu [1, 2]; Hai-Lin Yong [1, 2]; Liang Zhang [2, 3]; Sheng-Kai Liao [1, 2]; Juan Yin [1, 2]; Wei-Yue Liu [1, 2]; Wen-Qi [...]

Quantum key distribution (QKD) uses individual light quanta in quantum superposition states to guarantee unconditional communication security between distant parties. However, the distance over which QKD is achievable has been limited to a few hundred kilometres, owing to the channel loss that occurs when using optical fibres or terrestrial free space that exponentially reduces the photon transmission rate. Satellite-based QKD has the potential to help to establish a global-scale quantum network, owing to the negligible photon loss and decoherence experienced in empty space. Here we report the development and launch of a low-Earth-orbit satellite for implementing decoy-state QKDa form of QKD that uses weak coherent pulses at high channel loss and is secure because photon-number-splitting eavesdropping can be detected. We achieve a kilohertz key rate from the satellite to the ground over a distance of up to 1,200 kilometres. This key rate is around 20 orders of magnitudes greater than that expected using an optical fibre of the same length. The establishment of a reliable and efficient space-to-ground link for quantum-state transmission paves the way to global-scale quantum networks., Author(s): Sheng-Kai Liao [1, 2]; Wen-Qi Cai [1, 2]; Wei-Yue Liu [1, 2]; Liang Zhang [2, 3]; Yang Li [1, 2]; Ji-Gang Ren [1, 2]; Juan Yin [1, 2]; Qi [...]

Networks of optical clocks find applications in precise navigation1,2, in efforts to redefine the fundamental unit of the ‘second’3–6 and in gravitational tests7. As the frequency instability for state-of-the-art optical clocks has reached the 10−19 level8,9, the vision of a global-scale optical network that achieves comparable performances requires the dissemination of time and frequency over a long-distance free-space link with a similar instability of 10−19. However, previous attempts at free-space dissemination of time and frequency at high precision did not extend beyond dozens of kilometres10,11. Here we report time–frequency dissemination with an offset of 6.3 × 10−20 ± 3.4 × 10−19 and an instability of less than 4 × 10−19 at 10,000 s through a free-space link of 113 km. Key technologies essential to this achievement include the deployment of high-power frequency combs, high-stability and high-efficiency optical transceiver systems and efficient linear optical sampling. We observe that the stability we have reached is retained for channel losses up to 89 dB. The technique we report can not only be directly used in ground-based applications, but could also lay the groundwork for future satellite time–frequency dissemination.By using 1 W optical frequency combs and nanowatt-level linear optical sampling modules, a time–frequency dissemination over a free-space link of 113 km is achieved with a stability of less than 4 × 10−19 at 10,000 s. [ABSTRACT FROM AUTHOR]

A new method for fabricating microfluidic device on a piezoelectric substrate is presented. Wires are pasted by mushy starch and heated in a thermotank for microchannel patterns, which is then lightly placed in a small groove. Polydimethylsiloxane (PDMS) is filled in the small groove. The wires are drawn off after PDMS has been solidified. The PDMS microfluidic channel is then mounted on the piezoelectric substrate. Fluidic transportation and dilution operation are demonstrated for verifying the function of the microfluidic device. Results show that 6uL red ink droplet can be transported and diluted in the channels at 27.8dBm electric signal power. [ABSTRACT FROM AUTHOR]

A new normally open valve is presented. A polydimethylsiloxane (PDMS) cavity with two microchannels were fabricated using soft lithography technology. The one end of the cavity is arc-shaped at the joint with the microchannel. A steel ball is placed into the PDMS cavity mounted on a piezoelectric substrate with an interdigital transducer (IDT). Surface acoustic wave excited by the IDT is used for driving the steel ball to the arc area, leading to blocking the inlet of the microchannel. The microvalve was then closed. The switching characteristics were experimentally demonstrated using red ink solution. [ABSTRACT FROM AUTHOR]

A new method for dispatching microfluid is presented. A steel ball of 2mm diameter is placed on a 128 degrees YX LiNbO3 substrate. A PDMS frame is mounted on the piezoelectric substrate for defining the movement trajectory of the steel ball. Paper testing zone is fixed on a PDMS block for the target of the microfluidic dispatch. The steel ball is driven by surface acoustic wave, and carried microfluid at the outlet of the PDMS microchannel to the paper testing zone. Red ink solution is used to demonstrate the fluid dispatch. [ABSTRACT FROM AUTHOR]

The climbing phenomenon of fluid driven by surface acoustic wave was discovered, and its climbing characteristic was experimentally studied. A steel ball was fixed on an YX-128° LiNbO3 piezoelectric substrate by help of polydimethylsiloxane at the bottom of the steel ball. The fluid was forced by the acoustic streaming force and the resistance from the steel ball, leading to climbing the steel ball. The climbing characteristic was investigated using red ink solution. Results show that 3 µL red ink solution can climb the top of the steel ball with 2 mm diameter at 28.7 dBm electric signal power. [ABSTRACT FROM AUTHOR]

A new paper-based microfluidic device is fabricated on a piezoelectric substrate. A polydimethylsiloxane channel filled with cotton threads is mounted on the piezoelectric substrate with an interdigital transducer. A testing filter paper with dried reaction solution is coated on the end of the cotton thread. Sample solution is driven to the cotton thread channel and transported to testing area for microfluidic analysis. Red ink solution and color development reaction of starch are demonstrated for microfluidic operation and analysis. Results show that the linear velocity of microfluidic transportation in the cotton thread channel is 4.558 mm/s, and color development reaction of starch is successfully implemented. [ABSTRACT FROM AUTHOR]

A new microvalve controlled by surface acoustic wave was presented. A shape memory alloy (SMA) with plastic sheet was integrated into a printed circuit board by way of small copper pipe. A 128°-YX LiNbO3piezoelectric substrate was under the SMA wire with small gap. A polydimethylsiloxane (PDMS) microchannel was squeezed by the extension of the heated SMA wire due to surface acoustic wave radiation. The microvalve state was then changed. Experimental results show that the switching-off time of the microvalve is 39.533 s at 28.5 dBm electric signal power. The variation of SMA size during expansion is theoretically calculated. [ABSTRACT FROM PUBLISHER]

In the past, long-distance free-space quantum communication experiments could only be implemented at night. During the daytime, the bright background sunlight prohibits quantum communication in transmission under conditions of high channel loss over long distances. Here, by choosing a working wavelength of 1,550 nm and developing free-space single-mode fibre-coupling technology and ultralow-noise upconversion single-photon detectors, we have overcome the noise due to sunlight and demonstrate free-space quantum key distribution over 53 km during the day. The total channel loss is ∼48 dB, which is greater than the 40 dB channel loss between the satellite and ground and between low-Earth-orbit satellites. Our system thus demonstrates the feasibility of satellite-based quantum communication in daylight. Moreover, given that our working wavelength is located in the optical telecom band, our system is naturally compatible with ground fibre networks and thus represents an essential step towards a satellite-constellation-based global quantum network. [ABSTRACT FROM AUTHOR]

A new shape memory alloy (SMA) microvalve, which is switched on or off by surface acoustic wave, is presented. Two interdigital transducers with 27.5 MHz center frequency respectively are fabricated on a 1280yx-LiNbO3piezoelectric substrate for exciting surface acoustic waves. The surface acoustic waves are used for heating a paraffin oil droplet to raise the temperature of the SMA wire due to heating conduction. The spread distance of the two end of the SMA wire is then increased, which squeezed the polydimethylsiloxane (PDMS) microchannel connected with one end of the SMA wire by fixing the other end of the SMA wire in a printed circuit board. The microvalve is then switched off. Only removing the electrical signal off, the SMA wire is recovered softness state, and the fluid in the microchannel can then be transported driven by a syringe. The microvalve is switched on again. Red liquid is used to demonstrate the switching operation of the microvalve. Results show that the switching time of the microvalve is less 46s. The work is helpful for piezoelectric microfluidic devices for biochemical analysis. [ABSTRACT FROM PUBLISHER]

The attenuation characteristics of poly(dimethylsiloxane) (PDMS) film to surface acoustic wave was studied. An interdigital transducer with 27.7 MHz center frequency was fabricated on a 1280yx-LiNbO3substrate using microelectric technology. PDMS film with different thickness was coated on the piezoelectric substrate. Paraffin oil was pipetted on the PDMS film and heated by surface acoustic wave radiation. The temperature of the paraffin oil was measured by a temperature measuring meters. Then, the energy radiated into the paraffin oil per unit time was calculated. Comparison to SAW without the attenuation of PDMS film, the attenuation of SAW is 12.6%, 31.6% and 38% respectively, when the thickness of the PDMS film is 50μm, 100μm or 150μm. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) provides the only intrinsically unconditional secure method for communication based on the principle of quantum mechanics. Compared with fibre-based demonstrations, free-space links could provide the most appealing solution for communication over much larger distances. Despite significant efforts, all realizations to date rely on stationary sites. Experimental verifications are therefore extremely crucial for applications to a typical low Earth orbit satellite. To achieve direct and full-scale verifications of our set-up, we have carried out three independent experiments with a decoy-state QKD system, and overcome all conditions. The system is operated on a moving platform (using a turntable), on a floating platform (using a hot-air balloon), and with a high-loss channel to demonstrate performances under conditions of rapid motion, attitude change, vibration, random movement of satellites, and a high-loss regime. The experiments address wide ranges of all leading parameters relevant to low Earth orbit satellites. Our results pave the way towards ground-satellite QKD and a global quantum communication network. [ABSTRACT FROM AUTHOR]