In search of a more precise measurement of quantum phases, researchers from the University of Science and Technology of China have demonstrated a new measurement method that relies on multi-photon entanglement and the interference effect it generates.“High resolution quantum phase measurements will help to measure other related physical parameters with high precision, such as time shift, distance, etc.,” physicist Fangwen Sun told PhysOrg.com. Sun is currently with the Optical Nanostructure Laboratory at Columbia University in New York.In their study, which is published in a recent issue of Europhysics Letters, Sun and his colleagues describe an experiment where they achieve a phase measurement precision that surpasses the standard quantum limit, and nearly reaches the Heisenberg limit. “The scheme can be generalized to high-photon-number states,” Sun said. “There is no fundamental obstacle to achieve the precision approaching the Heisenberg limit.”As the researchers explain, the standard quantum limit is not the ultimate limit for measurement precision of quantum phases. Using a technique called squeezed-state-based interferometry, previous studies have already surpassed the standard quantum limit. However, the Heisenberg limit is considered the ultimate limit. Although researchers have proposed a number of schemes to approach this limit, none have been realized due an effect called loss.“The standard quantum limit is achieved with a regular source of light such as a laser,” Sun explained. “It goes as 1/N1/2 for N photons. The Heisenberg limit goes as 1/N for N photons. It can be achieved with quantum sources of light that exhibit special entanglement properties.” But, he added, “It has been proven that the Heisenberg limit is the true quantum limit and cannot be surpassed.”In their experiment, the researchers designed a method that is not as sensitive to loss as the previous proposals, and so it has a higher probability of resulting in an extremely precise measurement. First, the physicists generated an entangled state by injecting a two-photon Fock state into a beam splitter. Then, the entangled photons traveled through a line of optical elements including a half-wave plate, interference filter, and phase shifter. At the end, the physicists used a recently developed method called quantum state projection to extract the phase information from the entangled photons. “It is the collective effect of all the photons that improves the precision,” Sun said, explaining why better photon entanglement results in higher precision measurements. “The higher entanglement, the more collective effect.”With their new measurement technique, the researchers achieved a phase measurement precision of 0.506 for a two-photon state and 0.291 for a four-photon state. By contrast, the precision values set by the standard quantum limit are 0.707 and 0.5, respectively. For comparison, the Heisenberg limit has values of 0.289 and 0.25, which are thought to be impossible to achieve.Nevertheless, the physicists hope that, with anticipated improvements in technology leading to more efficient multi-photon detectors, the measurements might yield even more precise results. More information: Sun, F. W.; Liu, B. H.; Gong, Y. X.; Huang, Y. F.; Ou, Z. Y., Guo, G. C. “Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement.” Europhysics Letters, 82 (2008) 24001. Copyright 2008 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Citation: Measurement precision beats standard quantum limit (2008, April 21) retrieved 18 August 2019 from https://phys.org/news/2008-04-precision-standard-quantum-limit.html
Spin waves are where the electronic spin of one atom is transferred to another and then to another and so on propagating through a group. In this new research, the team found that by embedding information in a spin wave, and then retrieving it later, they could take advantage of the time it takes for the propagation to occur all the way though all of the atoms, thus allowing for holding onto quantum state information for a specified period of time.To make this come about, the team built a magneto-optical trap that first slowed atoms down using a laser beam. Once slowed, the atoms were held steady using magnets in a vertical triangular trap. When a photon was introduced, it caused a spin that was propagated through the atoms, creating a spin wave. At the other end, another laser fired at the same frequency as the first but with the opposite polarization caused the spin to be converted back into a photon, which revealed the quantum state information that had been held first in the original photon, and then conveyed through the wave. Using this technique, the team found that they could hold on to the quantum state information for 3.2 milliseconds and that the process was between seventy one and seventy five percent efficient.What’s more, the team believes that if optical lattices were introduced into the trap, i.e. crossed laser beams with different frequencies, they could make the whole system even more efficient. They also believe that this new process could be used as a means for creating memory storage in an actual quantum computer. More information: Efficient and long-lived quantum memory with cold atoms inside a ring cavity, Nature Physics (2012) doi:10.1038/nphys2324AbstractQuantum memories are regarded as one of the fundamental building blocks of linear-optical quantum computation and long-distance quantum communication. A long-standing goal to realize scalable quantum information processing is to build a long-lived and efficient quantum memory. There have been significant efforts distributed towards this goal. However, either efficient but short-lived or long-lived but inefficient quantum memories have been demonstrated so far. Here we report a high-performance quantum memory in which long lifetime and high retrieval efficiency meet for the first time. By placing a ring cavity around an atomic ensemble, employing a pair of clock states, creating a long-wavelength spin wave and arranging the set-up in the gravitational direction, we realize a quantum memory with an intrinsic spin wave to photon conversion efficiency of 73(2)% together with a storage lifetime of 3.2(1) ms. This realization provides an essential tool towards scalable linear-optical quantum information processing.via Arstechnica This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Quantum memory for communication networks of the future Journal information: Nature Physics (Phys.org) — One of the main sticking points to creating a true quantum computer capable of performing meaningful work, is the problem of storing quantum state information in memory. Recent efforts have resulted in highly efficient memory that lasted only a short time or low efficient memory that lasts longer. Now, a combined group of two teams, one from China and one from Germany, have come up with a way that appears to offer the best of both worlds. As they describe in their paper published in the journal Nature Physics, they found that they were able to store quantum information in atomic spin waves. Citation: Research group creates longer lived and more efficient quantum memory (2012, May 30) retrieved 18 August 2019 from https://phys.org/news/2012-05-group-longer-efficient-quantum-memory.html © 2012 Phys.Org Explore further
New Delhi: The Delhi unit of the BJP on Monday protested against the West Bengal government over the killings of party workers and leaders in the state. Hundreds of Delhi Bharatiya Janata Party (BJP) workers staged a protest outside Banga Bhawan here and raised slogans against West Bengal Chief Minister and Trinamool Congress chief Mamata Banerjee. The party workers also carried placards reading ‘stop political killings against RSS-BJP workers’, ‘stop political violence in Bengal’ and ‘why silence on Bengal political violence’. South Delhi MP Ramesh Bidhuri told IANS: “Mamata Banerjee is plotting the murder of BJP and RSS (Rashtriya Swayamsewak Sangh) workers,” adding it is being done to terrorise the people of the state. He also said that this year, over 20 people have died in West Bengal since Panchayat elections and slammed leaders of other parties over their silence on the issue.
Kolkata: A 42-year-old man has been arrested for attempting to rape a minor girl in his locality. The incident occurred at Tilajala on Thursday evening.According to police, the accused, Seikh Riazuddin, lured the victim with various promises and took her to his house. He tried to sexually assault the minor. The girl, however, was saved in due time as she screamed out for help, which immediately prompted the locals to come toher rescue.The victim has alleged that the man tried to touch her inappropriately, which left an injury mark on Also Read – Rain batters Kolkata, cripples normal lifeher body.The victim later fell ill and she was rushed to Calcutta National Medical College for treatment. The incident also triggered tension in the locality with locals staging a demonstration demanding stern action against the accused.The victim’s family members lodged a complaint at the local police station on Thursday night on the basis of which police have arrested Riazuddin on Friday morning.It was learnt that medical tests have confirmed that the girl was assaulted physically. The accused has been booked under Pocso Act.The victim girl is stated to be in a stable condition, the hospital sources said.The accused has been remanded to police custody after being produced before a court in the city.
Kolkata: A fresh low-pressure area that has been created over North Odisha and adjoining Bengal would bring moderate to heavy rainfall in various parts of the state, the Regional Meteorological Centre at Alipore predicted. However, the city may receive light to moderate rainfall in the next three days while some districts will witness heavy to very heavy rain. North-Eastern states are expected to see moderate rains in the next few days. States like Jharkhand, some parts of Bihar and Sikkim may also witness light to moderate rains. According to a senior weather official, the low pressure which was currently situating over North Odisha and adjoining parts of Bengal has gained some strength as a result of which various districts — both in North and South Bengal — will receive moderate to heavy showers depending on their geographical locations.
Kolkata: The state government on Monday informed the Calcutta High Court that hawkers in Salt Lake Sector V area will be relocated elsewhere only after the state has a hawker policy in place. Soon after hearing the state’s stand, the High Court stayed the process of evicting the hawkers encroaching upon the bus route of Sector V till August 30. The stay of Justice Debangshu Basak came in the wake of the Salt Lake Sector V Hawkers’ Welfare Association, moving the high court against the eviction order. Also Read – Rain batters Kolkata, cripples normal lifeThe next hearing in this regard will be held on August 23. The counsel appearing on behalf of the state claimed that the government is absolutely against forcible eviction and wants proper rehabilitation of the hawkers. Hawkers in Salt Lake Sector V were taken to two plots of land in the area on Saturday where the Nabadiganta Industrial Township Authority plans to relocate them. It may be mentioned that police wants the hawkers on Ring Road, the stretch from the SDF intersection in GN Block to Technopolis building to be vacated for smooth traffic movement. It may be mentioned that hawkers in Sector V had demonstrated by keeping their shops closed on Friday to protest the order asking them to clear three main thoroughfares or face eviction. They also allegedly prevented several delivery persons of app-based food delivery services on their way to offices in Sector V.
It is a three day extravaganza aiming to represent Delhi as a perfect tourist destination by showcasing and promoting its cultural and culinary diversity. The fest will be celebrating the irresistible fruit – mango, while also encouraging the cultural importance of Mangoes associated with Delhi. The celebration will continue for the three days of the fest.The festival will be inaugurated by Arvind Kejriwal, Chief Minister of Delhi in the presence of Manish Sisodia, Dy. Chief Minister, Delhi and Kapil Mishra, Minister for Tourism, Delhi. The fiesta will see a grand opening with artists from all over the country performing on stage and mascots dressed up in different costumes, giving it an extravagant look. Various summer fruit cultivators, product manufacturers, sharbat and dessert manufacturers and distributors from different regions of the country will be a part of this grand event. Also Read – ‘Playing Jojo was emotionally exhausting’The venue, Dilli Haat, Janakpuri corresponds to the essence of the fete. It is a multi-purpose, socio-cultural complex with a bazaar-like feel to it. It is an urban version of the traditional weekly market, with a delightful mix of craft, cuisine and culture. The Delhi Summer Festival is the perfect spot for all foodies to treat their taste buds with various summer fruits, thirst quenchers, desserts and much more.It will not only be a visual and mouth-watering treat, but also a jubilation of summer with taste and fun. Guests will see stage performances by ‘Twirls & Thumkas’ enacting a parade act along with other artists like Abhijit Ganguly, a comedian, Abhishek Acharya, an illusionist, Pratyul Joshi, a musician. These performances will be conducted throughput the event. Various amateur bands, singers, musicians have also been invited to perform at the gala. Also Read – Leslie doing new comedy special with NetflixGuests will also get to attend interactive classes where recipes of yoghurt, sharbats, smoothies will be taught.Several competitions will make sure the visitors make the most out of the Summer Fest. A unique initiative ‘100 ka hai daam, kitne bhi khao Aam’ has been taken by the organizers in which the visitors have to pay only Rs.100 per entry and can eat mangoes at their heart’s desire. ‘Hangout’ is an exclusive jungle-themed entertainment centre, furnished with various games and activities to keep the children engaged.
Kolkata: One more person identified as Jaydev Yadav has been arrested in connection with the murder of Ultandanga housewife Archana Palangdar and her lover Balaram Keshri.He was arrested on Saturday night and was brought to Kolkata and produced before a city court on Sunday. Jaydev has been remanded to police custody till December 27. Sources informed that Jaydev used to be the manager of the hotel where Archana and Keshri stayed. After the murder case came to light, Jaydev Also Read – Rain batters Kolkata, cripples normal lifefled Kolkata. During investigation, the sleuths came to know that both Archana and Keshri’s body were removed from the hotel using an app cab. An employee identified as Ashis Yadav loaded the bodies in the cab with assistance from two other people identified as Harihar Mahato and Yadu Prasad. All of them were arrested during an investigation. During interrogation of Ashis, the sleuths came to know about Jaydev’s involvement. According to the sources, Jaydev being the manager of the hotel had asked Ashis to dispose of the bodies overnight. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedAshis then booked an app cab and did as he was directed by Jaydev. On sensing danger, Jaydev vanished from Kolkata. After sleuths came to know about Jaydev’s involvement, they tried to locate him but failed. Recently, with the help of the mobile phone tower location tracking system, police got information that Jaydev was hiding in Jharkhand. A few days ago, police became sure of his location and sent a team to Jharkhand for arresting Jaydev. On Saturday night, the police team successfully nabbed Jaydev and brought him to Kolkata. Archana and Keshri were found dead inside a hotel room on September 19. Later, Archana’s body was dumped in a canal near Chowbaga pumping station and Keshri’s body was dumped at Nonadanga adjacent to Eastern Metropolitan (EM) Bypass. On September 20, Archana’s body was fished out of the canal and a few days after, police were able to recover Keshri’s body. Later, cops came to know about the New Market hotel where they had stayed. During an investigation, the sleuths arrested several persons connected to the hotel and came to know that Keshri murdered Archana over some conflict and committed suicide. However, police are not believing the story narrated by them. It is expected that after Jaydev’s interrogation, a detailed information related to the murder case would be revealed.