Home › Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe › 4. Assessment of current results and outlook on future efforts › 4.1 Quantum Communication

4.1.7 New Applications and Protocols

Tue, 2010-03-02 14:48 - Daniele Binosi
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Approach and perspectives

The field of quantum communication is still very young, having been essentially unknown until 20 years ago. As such, one should expect new ideas and leave open space for fundamental research. From the theoretical point of view, there are several problems that have to be considered in the context of quantum communication. First of all, since the field is still very young, one should expect new applications related to both efficiency and secrecy in communication. Examples of the first can be connected to secret voting protocols, digital signatures, or fingerprinting. Examples of the second field could be, for example, connected to dense coding, or agenda protocols. Apart from that, there are still many open theoretical questions of crucial importance for quantum cryptography. These are related to the tolerance to noise of current protocols (both with one and two way communication), the connection between single photon and continuous variable protocols, and the search for more efficient and faster ways of distributing keys and quantifying their security. 

Quantum communication protocols can be often understood as entanglement manipulation protocols. An important class of these protocols delivers classical data with properties derived from the underlying quantum state. For this class the question arises whether one can replace the quantum manipulation and subsequent measurement by another two-step procedure that first measures the quantum states and then performs classical communication protocols on the resulting data to complete the task. Such an approach would be preferential in real implementations, as is illustrated in the case of quantum key distribution. It is important to study under which circumstances such a replacement can be done. 
A relatively new idea could be using quantum memories to perform local operations and store the results while the classical communication is going on in communication protocols, which require local operations and classical communication (LOCC) are required. Transforming ideas of percolation to quantum networks has been a relatively new concept but one that also opens some fascinating possibilities for network distribution of entanglement.
 
European groups working in this field include: A. Acin (ICFO, ES), N. Brunner, N. Gisin and N. Sangouard (Geneva, CH), H. Buhrman (Amsterdam, NL), N. Cerf, S. Massar and S. Pironio (Brussels, BE), I. Damgard (Aarhaus, DK), M. Peev (AIT, AT), R. Renner (Zurich, CH), R. Werner (Braunschweig, D).
 

State of the art

Important progress has been made in developing new protocols for quantum repeater architectures. A key concept that was recently introduced was the multimode capacity of quantum memories, which allows orders of magnitude increases in distribution rates [1]. Combining this with approaches that serialise distribution and even reduced the need for quantum memories [2] may hold the potential for high rates and long distance. The concept of heralded photon amplifiers opens up new possibilities for distributing quantum resources, for example, DI-QKD [3] and heralded quantum memories for quantum repeaters [4] both in the context of secure communication however these concepts should find a much broader field of applications.  The possibility of a cheat sensitive quantum protocol to perform a private search on a classical database [5] have also been proposed and recently experimental demonstrated [6]. A return to some of the foundational concepts of QIPC has seen Bell inequalities find renewed importance for so-called "Device Independent" security [7] and the concept of device independent quantum infomation processing is finding applications far beyond QKD (see Section 4.3).
 
Challenges

The main challenges for new applications and protocols are:

  • Investigate new protocols for QKD and beyond, possibly inspired by existing protocols as well as systems that combine aspects of discrete and continuous variable operation;
  • Develop new quantum repeater protocols that are robust with respect to loss and low component efficiencies and explore new verification strategies for multipartite quantum networks;
  • Break with the paradigm that noise is necessarily harmful and innovate tools of state engineering and quantum information protocols based on noise and measurements.

Key references
[1] C. Simon et al., Phys. Rev. Lett. 98, 190503 (2007)
[2] W. J. Munro, Nature Photonics 6, 777 (2012)
[3] N. Gisin, S. Pironio and N. Sangouard, Phys. Rev. Lett. 105, 070501 (2010)
[4] J. Minar, H. de Riedmatten and N. Sangouard, Phys. Rev. A 85, 032313 (2012)
[5] V. Giovannetti et al. Phys. Rev. Lett. 100, 230502 (2008)
[6] M. Jakobi et al., Phys. Rev. A 83, 022301 (2011)
[7] A. Acin et al., Phys. Rev. Lett. 98, 230501 (2007)