Continuous variable quantum key distribution (CVQKD) uses the continuous quadratures of light to share a secret key between a transmitter and receiver. The presence of an eavesdropper can be detected by fundamental quantum mechanics. Compared to the more established discrete variable QKD, CVQKD uses more cost-effective homodyne detectors which are more compatible with current telecommunication technologies. In a future global quantum network, CVQKD could be used to ensure the secure exchange of information. In this work, the feasibility of a variety of CVQKD protocols in different channels that could be used to establish a global quantum network are studied. These are the Gaussian modulated and discrete modulated CVQKD protocols for satellite to optical ground station downlinks and uplinks for Earth-space connections, inter-satellite links for space connections, satellite to ship and underwater links for maritime connections, and fibre network links for terrestrial connections. Secret key distribution between continents and various regions is simulated while accounting for the different adverse effects associated with each link. The combination of these connections with routing and scheduling ensures inter-continental high-speed information exchange with unconditional security that is required to achieve the goal of a global quantum network.
Continuous variable quantum key distribution (CVQKD) is the sharing of a secret key between parties using the continuous quadratures of light, the phase and amplitude quadratures, which can infer the presence of an eavesdropper using fundamental quantum mechanics. A significant performance inhibitor of free-space CVQKD is turbulence which gives rise to optical wavefront distortions consisting of random phase and amplitude fluctuations (scintillation). In this work, we experimentally study the negative effects of turbulence on coherent states in a free-space channel for CVQKD. We demonstrate during coherent state transmissions from a continuous-wave laser in a turbulent channel, the interferometric visibility between a local oscillator and signal fluctuates and decreases with higher degrees of scintillation. This leads to the breaking of the phase-lock between the local oscillator and quantum signal and a decrease in the secret key rate (SKR). By incorporating an adaptive optics system, the degraded optical wavefront from turbulence can be corrected using a closed-feedback loop. This leads to the stabilisation and reduction in the decrease of the interferometric visibility in a turbulent channel. The improvement provided by adaptive optics leads to the increased performance of CVQKD, resulting in positive SKRs, which would have otherwise been infeasible in a turbulent channel.
Satellites have the potential to support quantum communication over much longer distances than fibre optics networks and, as a result, there is a large amount of investment globally in quantum communication satellites. The Australian National University Optical Ground Station aims to provide ground services support for quantum communication satellites, and enhance the quantum link performance by the use of Adaptive Optics techniques. Numerical simulations have been carried out to assess the advantage of correcting the atmospheric turbulence on quantum downlinks with Adaptive Optics. Fibre coupling efficiency of the communications light onto a single mode fibre has been chosen as the performance metric. We pay special attention to the focusing optics and optimise them for the Single Mode Fibre coupling. We present the minimum requirements for an AO system to produce a significant improvement on the quantum link using off-the-shelf components. This paper gathers the main outcomes of the end-to-end numerical simulation and describes a potential pathway for future atmospheric corrected quantum communications.
Backward Brillouin scattering in whispering-gallery-mode micro-resonators offers an exciting avenue to pursue both classical and quantum optomechanics applications. Our team—the Quantum Measurement Lab—together with our collaborators, are currently utilizing this regime and the favourable properties it affords for non- Gaussian motional state preparation of the acoustic field. In particular, the high mechanical frequencies, and low optical absorption and heating provide a promising route to overcome current hindrances within optomechanics. Three of our recent experimental results in this area include: (i) Brillouin optomechanical strong coupling, (ii) single-phonon addition or subtraction to a thermal state of the acoustic field, and (iii) performing phase-space tomography of non-Gaussian states generated by single- and multi-phonon subtraction. This SPIE presentation will cover these three results, what they enable, and the broader direction of our lab including the prospects of this platform for quantum-memory applications.
Satellite-based optical quantum technologies represent a promising field for obtaining a worldwide quantum network. However, due to the limited size of satellites and the adverse conditions of a space environment, only compact and resistant devices can be used for this purpose. In this respect, we present for the first time the space qualification of integrated photonic circuits fabricated by Ultrafast Laser Writing. By inscribing different straight waveguides, directional couplers and Mach-Zehnder interferometer, and by exposing them to appropriate proton and gamma ray irradiations, we show that our integrated devices are suited for performing quantum experiments in a low Earth orbit.
Quantum optomechanics with acoustic waves is an emerging new area within optomechanics with significant potential to engineer and utilize quantum states at a macroscopic scale. In this talk, a Brillouin optomechanical platform will be discussed that unites several favorable properties including high mechanical frequency (~ 10 GHz), very low optical loss and absorption, and back-scatter operation, thus offering a promising route to circumvent existing experimental challenges. Using this system, we (i) observe Brillouin optomechanical strong coupling between the optical cavity field and these high-frequency mechanical vibrations, which enables optical control at a rate that exceeds the system's decay rates, and (ii) perform heralded single-phonon addition and subtraction to a mechanical thermal state, which has the counterintuitive effect of approximately doubling the mean thermal occupation. Having both capabilities provides a powerful toolkit for quantum control with phonons.
Entanglement distillation is an indispensable ingredient in extended quantum communication networks. Distillation
protocols are necessarily non-deterministic and require non-trivial experimental techniques such as noiseless
amplification. We show that noiseless amplification could be achieved by performing a post-selective filtering of
measurement outcomes. We termed this protocol measurement-based noiseless linear amplification (MBNLA).
We apply this protocol to entanglement that suffers transmission loss of up to the equivalent of 100km of optical
fibre and show that it is capable of distilling entanglement to a level stronger than that achievable by transmitting
a maximally entangled state through the same channel. We also provide a proof-of-principle demonstration
of secret key extraction from an otherwise insecure regime via MBNLA. Compared to its physical counterpart,
MBNLA not only is easier in term of implementation, but also allows one to achieve near optimal probability of
success.
Here we show that the photon echo equivalent of an NMR gradient echo is completely efficient if the sample is
optically thick, the detunings of the atoms vary linearly along the direction of propagation and the storage time
is short compared to the decay rate of the atoms. In this process the only light that interacts with the sample
of atoms during the storage and retrieval process is the light that is to be stored and then retrieved, their are
no auxiliary beams. The stored and recalled light travel in the same direction and their is no need for the phase
matching operation that is present in previous quantum memory proposals using controlled inhomogeneous
broadening. This greatly simplifies various possible implementations. We present analytical, numerical and
experimental results of this scheme. We report experimental efficiencies of up to 15% and suggest simple realizable
improvements to significantly increase the efficiency.
We experimentally demonstrate a complete, end-to-end, quantum key distribution system using a continuous wave laser and standard optical components. Our implementation encodes random bits as weak Gaussian modulations onto the phase and amplitude quadratures of the laser beam. We process data from the quantum channel using a post-selection procedure and subsequently apply information reconciliation and privacy amplification procedures to generate an absolutely secure secret key. The maximum information that an eavesdropper may have obtained about this secret key, from the quantum channel and classical communications, is bounded to below one bit. Under the assumption of individual Gaussian eavesdropping attacks, we achieve a secret key generation rate of 25 Mbits/s for a lossless channel and 1 kbit/s for 90% channel loss, per 17 MHz of detected bandwidth.
We demonstrate a multipartite protocol that utilizes entanglement to securely distribute and reconstruct a quantum state. A secret quantum state is encoded into a tripartite entangled state and distributed to three players. By collaborating together, a majority of the players can reconstruct the state, whilst the remaining player obtains nothing. This (2,3) threshold quantum state sharing scheme is characterized in terms of fidelity (F), signal transfer (T) and reconstruction noise (V). We demonstrate a fidelity averaged over all reconstruction permutations of 0.73 ± 0.04, a level achievable only using quantum resources.
We present an experimental scheme to perform continuous variable (2,3) threshold quantum secret sharing on the quadratures amplitudes of bright light beams. It requires a pair of entangled light beams and an electro-optic feedforward loop for the reconstruction of the secret. We examine the efficacy of quantum secret sharing in terms of fidelity, as well as the signal transfer coefficients and the conditional variances of the reconstructed output state. We show that, in the ideal limit, perfect secret reconstruction is possible. We discuss two different definitions of quantum secret sharing: the sharing of a quantum secret and the sharing of a classical secret with quantum resources.
The quantum nature of light imposes a limit to the detection of all properties of a laser beam. We show how we can reduce this limit for a measurement of the position of a light beam on a quadrant detector, simultaneously in two tranverse directions. This quantum laser pointer can measure the beam direction with greater precision than a usual laser. We achieve this by combining three beams, one intense coherent and two vacuum squeeezed beams, with minimum losses into one spatially multimode beam optimized for this application.
We present methods of transforming the standard quadrature amplitude squeezing of a continuous-wave light beam to its Stokes parameters and transverse spatial modes statistics. These two states of light are called polarization squeezing and spatial squeezing, respectively. We present experimental results of the quadrature amplitude, polarization and spatial squeezing obtained with a common experimental setup based on optical parametric amplifiers. The transformations from quadrature amplitude to polarization and spatial squeezing are achieved with only simple linear optics.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.