High Photon Information Efficient Imaging using Single Photon Source
Reihaneh Shahrokhshahi, Niranjan Sridhar, Olivier Pfister, Saikat Guha, Jonathan L. Habif, Aaron Miller, Adriana E. Lita, Brice Calkins, Thomas Gerrits, Antı́a Lamas-Linares, Sae Woo Nam
We report progress towards information-efficient quantum imaging. We implemented a 4-mode interferometer (Fig.1) which uses both polarization and spatial encoding to image Hadamard-encoded phase arrays. We used this interferometer with a single-photon source to achieve the theoretical goal of Photon Information Efficiency (PIE)= 2 bits per photon (bpp). This demonstration is a particular case of a generalized M-path interferometer which can yield log2 M bits of information with a single measurement of a single photon, the photon being placed in the W state
We report progress towards information-efficient quantum imaging. We implemented a 4-mode interferometer (Fig.1) which uses both polarization and spatial encoding to image Hadamard-encoded phase arrays. We used this interferometer with a single-photon source to achieve the theoretical goal of Photon Information Efficiency (PIE)= 2 bits per photon (bpp). This demonstration is a particular case of a generalized M-path interferometer which can yield log2 M bits of information with a single measurement of a single photon, the photon being placed in the W state
Single photons are the smallest excitation states of the elctromagnetic field. They can be experimentally created but there is no apparatus that performs this task with 100% efficiency. Many techniques and theorems of optical quantum information theory use single photons. In order to utilize them for information processing, it is reasonable to know if they had been successfully produced. In other words: One needs heralded single photons. How to achieve this, is the main result of this diploma thesis. The task has been to improve the efficiency of already existing single photon sources. An apparatus had to be found which postprocesses the output of such sources in order to either herald the photons or at least to improve the efficiency. This apparatus is explicitly allowed to use other optical sources, for example coherent states (laser). The situation has been formally represented by the assumption that single photon sources produce a mixture of vacuum and the single photon state. It is known that experimental set-ups also create higher photon contributions. These contributions are considered to be small in corresponding publications. For some cases they even seem to vanish at all. One can distinguish two regimes concerning the techniques which have been used in this work: linear and nonlinear optics. Linear optical tools, for example the beam splitter, do not absorb photons in the ideal case, but it is not easy to implement useful transformations by their means. Absorption and weak coupling are drawbacks which arise mainly in nonlinear optical media. This work shows that the interactions two-photon absorption and cross phase modulation can be used in schemes, which enable the heralding of single photons. Already there are some linear optical quantum gates which manipulate optical states by means of single photons. Photons do not interact with each other directly, in contrast to electrons for example. Therefore quantum gates which act on more than one mode are interesting. The effective interaction of these gates is not quitecomparable to unitary dynamics. Moreover, these gates do not function in each case. Measurements required in auxiliary modes yield different results for each single case and in order to obtain the desired effect the cases have to be selected according to the measurement results. It has been investigated, how such gates perform if they have statistical mixtures as a resource instead of perfect single-photon states. Yet, no improvement of the single-photon contribution has been accomplished by means of these apparatuses. Hereby it has not been disproved that it is possible to achieve this goal using other apparatuses and techniques of linear optics. Yet, it has been shown that an enhancement is possible but then a non-vanishing two-photon contribution is appended. One of the most basic quantum gates is the conditional sign flip. The optical 8 interaction cross phase modulation acts in quite the same way considering only single photons. This effect enables the heralding of single photons in the ideal case. Within this work it has been shown that a Mach-Zehnder interferometer, a cross phase modulating medium and a photo-detector can be employed for this purpose. One could use any source of light as input to the interferometer but a strong coherent state (laser) may be preferred for the purpose of enhancing the interaction. The absorption of two-photon states is another non-linear effect. Astonishingly this effect serves to generate a heralded single-photon state given two imperfect single-photon sources. First the photon adding tool is employed which consists of a beam splitter and a photo-detector. By means of that and the statistical mixtures of two single-photon sources one creates a mixture which contains vacuum, the single-photon state and additionally the two-photon Fock state. This mixture propagates through a Mach-Zehnder interferometer. The interferometer is adjusted such that it is transparent for incoming light. In addition to the interferometer alone a two-photon absorbing medium is placed in one of its arms. For this reason there is a chance that the two-photon contribution entering the interferometer is absorbed within this medium. We cannot exclude this unfortunate case. A detector is placed in one of the two output modes. The interferometer is adjusted such that the single photon state does not leave in the mode in which the detector is placed, but always in the other mode. The detector can only click if the two-photon state propagates through the interferometer and if it is not destroyed in the absorbing medium. If the detector then receives one photon it is obvious that another one must leave in the other mode. The whole phenomenon is very similar to the concept of null measurement. Although not a main result, it has been shown here that the so-called Hong-Ou-Mandel effect can be generalized. It has been proven that the beam splitter transforms Fock states with equal Fock number into superpositions of Fock numbers which are even in each mode. Another effect on special odd Fock states is conjectured.
How to manipulate (operate or measure) single photons efficiently and simply is the basic problem in optical quantum information processing. We first present an efficient scheme to transform a biphoton polarization state to a corresponding single-photon state encoded by its polarization and spatial modes. This single-photon state carries both the information of the controlled and target photons. It will make the realization of bipartite positive-operator-valued measurements efficiently and simply. Moreover, the inverse transformation from the single-photon state back to the corresponding biphoton polarization state is also proposed. Using both the transformations, the realization of the arbitrary two-qubit unitary operation is simple with an M-Z interferometer. All the schemes are feasible with the current experimental technology.
Many important realizations and proposals for applications in quantum information processing require single photons as carriers of quantum information. Here, we review different demonstrations of quantum applications using a deterministic single-photon source based on InP/GaInP quan- tum dots. First, the single-photon generation is described and verified by autocorrelation measurements. A modification of the correlation setup allows the simultaneous observation of wave and particle properties of the photons. Additional to single-photon emission, photon pairs and triplets from multi- exciton cascades were observed, as well. Using a Michelson interferometer an efficient separation of photon pairs can be achieved allowing multiplexing on a single-photon level. The applicability was demonstrated in a quantum key distribution experiment. As another application, different degrees of freedom of a single photon were used to realize a two-qubit Deutsch-Jozsa algorithm. Encoding the quantum information in appropriate bases, an operation of the setup resistant to phase fluctuation was demonstrated.
Many important realizations and proposals for applications in quantum information processing require single photons as carriers of quantum information. Here, we review different demonstrations of quantum applications using a deterministic single-photon source based on InP/GaInP quantum dots. First, the single-photon generation is described and verified by autocorrelation measurements. A modification of the correlation setup allows the simultaneous observation of wave and particle properties of the photons. Additional to single-photon emission, photon pairs and triplets from multiexciton cascades were observed, as well. Using a Michelson interferometer an efficient separation of photon pairs can be achieved allowing multiplexing on a single-photon level. The applicability was demonstrated in a quantum key distribution experiment. As another application, different degrees of freedom of a single photon were used to realize a two-qubit Deutsch-Jozsa algorithm. Encoding the quantum information in appropriate bases, an operation of the setup resistant to phase fluctuation was demonstrated.
Quantum imaging usually refers to imaging that takes advantage of quantum entanglement to obtain results beyond the classically achievable limits [1]. Various complex experimental setups are used to obtain quantum images, and even more complex experimental setups are used when the goal is to record and retrieve the phase information of the object. Classical holography offers the possibility to record and retrieve phase information from a hologram [2]. However, in low-light conditions, a major challenge is to record images with a high signal-to-noise ratio. Classical schemes [3]–[5], of course, do not aim to demonstrate the quantum properties of the experiments, and quantum schemes [6]–[8] rely on complex preparation of the light beam and do not necessarily provide an advantage for holographic imaging. To date, no simple quantum scheme with quantum advantage has been developed for low-light holographic imaging.
The ability to reliably inscribe information on single photons is a crucial requirement for quantum applications such as quantum communication and measurement-based photonic quantum computation. Experimental implementations generally employ phase modulators in single-pass or Mach-Zehnder-interferometer configurations to encode information on photonic qubits. However, these approaches are intrinsically sensitive to environmental influences, which limits the achievable quantum error rates in practice, posing a major bottleneck in the transition of quantum applications with deterministic sources from the laboratory to the field. Inspired by the adaptation of Sagnac interferometer encoders for laser-based applications, we report a demonstration of a polarization encoder for single-photon qubits based on a free-space Sagnac interferometer. The device showcases inherent phase stability and overcomes previous error-rate limitations: Telecom-wavelength photons emitted by a quantum dot are modulated at a rate of 152 MHz and with a quantum bit error rate of 0.69 ± 0.02 % , marking the lowest value reported to date for MHz-rate information encoding on single photons by a factor of > 3 . This combination of low error rate, high modulation speed, stability, and operation with telecom-wavelength sub-Poissonian photons is an essential requirement for bringing quantum applications based on deterministic photon sources from the laboratory to the field and a significant step toward unlocking the full potential of a future quantum Internet.