Preparing arbitrary pure states of spatial qudits with a single phase-only spatial light modulator (original) (raw)

Manipulating spatial qudit states with programmable optical devices

Optics Express, 2009

The study of how to generate high-dimensional quantum states (qudits) is justified by the advantages that they can bring for the field of quantum information. However, to have some real practical potential for quantum communication, these states must be also of simple manipulation. Spatial qudits states, which are generated by engineering the transverse momentum of the parametric down-converted photons, have been until now considered of hard manipulation. Nevertheless, we show in this work a simple technique for modifying these states. This technique is based on the use of programmable diffractive optical devices, that can act as spatial light modulators, to define the Hilbert space of these photons instead of pre-fabricated multi-slits.

Quantum Key Distribution with Higher-Order Alphabets Using Spatially Encoded Qudits

Physical Review Letters, 2006

We present a proof of principle demonstration of a quantum key distribution scheme in higherorder d-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an average error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.

Quantum Communication without Alignment using Multiple-Qubit Single-Photon States

Physical Review Letters, 2007

We propose a scheme for encoding logical qubits in a subspace protected against collective rotations around the propagation axis using the polarization and transverse spatial degrees of freedom of single photons. This encoding allows for quantum key distribution without the need of a shared reference frame. We present methods to generate entangled states of two logical qubits using present day down-conversion sources and linear optics, and show that the application of these entangled logical states to quantum information schemes allows for alignment-free tests of Bell's inequalities, quantum dense coding and quantum teleportation.

Optical implementation of the encoding of two qubits to a single qutrit

Physical Review A, 2006

We have devised an optical scheme for the recently proposed protocol for encoding two qubits into one qutrit. In this protocol, Alice encodes an arbitrary pure product state of two qubits into a state of one qutrit. Bob can then restore error-free any of the two encoded qubit states but not both of them simultaneously. We have successfully realized this scheme experimentally using spatial-mode encoding. Each qubit (qutrit) was represented by a single photon that could propagate through two (three) separate fibers. We theoretically propose two generalizations of the original protocol. We have found a probabilistic operation that enables to retrieve both qubits simultaneously with the average fidelity above 90 % and we have proposed extension of the original encoding transformation to encode N qubits into one (N + 1)-dimensional system.

Linear-optics realization of channels for single-photon multimode qudits

Physical Review A, 2011

We propose and theoretically study a method for the stochastic realization of arbitrary quantum channels on multimode single-photon qudits. In order for our method to be undemanding in its implementation, we restrict our analysis to linear-optical techniques, vacuum ancillary states and non-adaptive schemes, but we allow for random switching between different optical networks. With our method it is possible to deterministically implement random-unitary channels and to stochastically implement general, non-unital channels. We provide an expression for the optimal probability of success of our scheme and calculate this quantity for specific examples like the qubit amplitudedamping channel. The success probability is shown to be related to the entanglement properties of the Choi-Jamio lkowski state isomorphic to the channel.

Teleportation of one ququat encoded in single mode superposition of coherent states

2012

Superposition of optical coherent states (SCS)   , possessing opposite phases, plays an important role as qubits in quantum information processing tasks like quantum computation, teleportation, cryptography etc. and are of fundamental importance in testing quantum mechanics. Recently, ququats and qutrits defined in four and three dimensional (D) Hilbert space, respectively, have attracted much more attention as they present advantage in secure quantum communication and also in researches on the foundation of quantum mechanics. Here, we show that superposition of four non-orthogonal coherent states   and  i  , that are 90 ο out of phase, can be employed for encoding one ququat defined in a 4D Hilbert space spanned by four newly defined multi-photonic states, j  with j n  4 , numbers of photons, where,. We propose a scheme which generates states 3 , 2 , 1 , 0  j j . When these states fall on a 50-50 beam splitter, the result is bipartite four-component entangled coherent state which represents equivalently an entangled ququat. Finally, we propose a linear optical scheme that gives almost perfect teleportation (minimum average fidelity) of single ququat encoded in SCS using entangled ququat based on coherent states with almost perfect success rate for coherent amplitude 99. 0  2. 3  . The present theoretical investigation and teleportation protocol is important in the sense that ququat allows the quantum information to be encoded and processed much more compactly and efficiently using fewer coupled quantum system.

Qudit-Teleportation for photons with linear optics

Scientific Reports, 2014

Quantum Teleportation, the transfer of the state of one quantum system to another without direct interaction between both systems, is an important way to transmit information encoded in quantum states and to generate quantum correlations (entanglement) between remote quantum systems. So far, for photons only superpositions of two distinguishable states (one "qubit") could be teleported . We here show how to teleport a "qudit", i.e., a superposition of an arbitrary number d of distinguishable states present in the orbital angular momentum of a single photon using d beam splitters and d additional entangled photons. The same entanglement resource might also be employed to collectively teleport the state of d/2 photons at the cost of one additional entangled photon per qubit. This is superior to existing schemes for qubits which require an additional pair of entangled photons per qubit.

Constructing Four-Photon States for Quantum Communication and Information Processing

International Journal of Theoretical Physics, 2008

We provide a method for constructing a set of four-photon states suitable for quantum communication applications. Among these states is a set of concatenated quantum code states that span a decoherence-free subspace that is robust under collective-local as well as global dephasing noise. This method requires only the use of spontaneous parametric down-conversion, quantum state post-selection, and linear optics. In particular, we show how this method can be used to produce all sixteen elements of the second-order Bell gem G 16 , which includes these codes states and is an orthonormal basis for the Hilbert space of four qubits composed entirely of states that are fully entangled under the four-tangle measure.

Implementation of quantum operations on single-photon qudits

Physical Review A, 2007

We show that a general linear transformation from one single photon qudit to another, the dimension of which can be either equal or unequal to that of the first one, can be implemented by linear optics. As an application of the scheme we elaborate a method to deterministically realize any finite-element Positive Operator Value Measure (POVM) on single photon signals, which is also generalizable to any quantum system in principle.

Measurement and control of spatial qubits generated by passing photons through double slits

Physical Review A, 2008

We present an experimental study of the non-classical correlations of a pair of spatial qubits formed by passing two down-converted photons through a pair of double slits. After confirming the entanglement generated in our setup by quantum tomography using separate measurements of the slit images and the interference patterns, we show that the complete Hilbert space of the spatial qubits can be accessed by measurements performed in a single plane between the image plane and the focal plane of a lens. Specifically, it is possible to obtain both the which-path and the interference information needed for quantum tomography in a single scan of the transversal distribution of photon coincidences. Since this method can easily be extended to multi-dimensional systems, it may be a valuable tool in the application of spatial qudits to quantum information processes.